Butterfly Effect was a convoluted time travel movie in which the hero, Evan Treborn, managed to ruin his own life and the lives of others around him by trying to fix things in the past.  It was laced with impossibilities, inconsistent with its own rules, and generally the kind of film that time travel fans love because they believe they can solve it, and keep working at it, despite the fact that it is insoluble.  Thus a sequel was made, Butterfly Effect 2, in which a new hero, completely unrelated to the original one, Nick Larson, discovers a similar ability, and so attempts to fix things in his own life, again with disastrous effects.  That one managed to find impossibilities that the original missed, as well as repeating several of the problems of its predecessor.  So they made a third, Butterfly Effect 3:  Revelations, and the question is whether it is as disastrous, temporally, as its predecessors.

This time the time traveler is Sam Reid, who with the advice of a physics professor named Harry Goldburg has adopted two important rules--one that he never changes his own past, and the other that he always has someone supervising his body when he jumps.  This is usually his little sister Jenna, who adores him.  Together they use his gift to solve unsolved murders, pretending he is a psychic.  He leaps back to the times and places of the murders and watches carefully, memorizing the details, so he can find the face in the mug shots and tell the police exactly what happened.  As the film opens he has led them to twenty-two killers, and is identifying his twenty-third.  We also know that prior to this he made a trip to the past to save Jenna from a fire--the main reason for his adherence to those rules, as his parents died in that fire instead, but he was fifteen at the time and had suffered through Jenna's funeral.  That implies that he already knew he could travel to moments in the past, and therefore that he had already done so.  We thus have at least twenty-four trips to the past prior to the opening of the movie, only one of which (the fire) we know in any detail.

As with the other films, the time traveler occupies his own younger body for the duration of his visit.  He did not suffer the blackouts of the first film, but we noted there that these were probably a separate symptom of the problem, and noted in the second film that Nick did not have these.  Sam, though, does not use photographs or movies or journals, but instead obtains the date, time, and place he is targeting and focuses on these as he loses touch with his present body.  That body is in a tub filled with ice water, apparently to prevent him from overheating, and when Jenna is monitoring him he is attached to a couple of leads on his forehead and chest, suggesting that brain and cardiac activity are being monitored.

Things start going wrong, though, when he breaks his rule.  A girl he knew in high school comes to see him, Elizabeth Brown, sister to his high school sweetheart Rebecca Brown who was murdered in her bedroom.  Lonnie Flennons, whom Rebecca was secretly seeing on the side, has been convicted of the crime, and now a decade later he is about to be executed for it--but Elizabeth has discovered in Rebecca's diaries enough to cause her to believe someone else killed her sister, and she wants the real killer identified before the wrong person is executed.  She offers to hire him.

He quite reasonably but without explanation declines, but it eats at him, and so he changes his mind, deciding that it would not be unreasonable for him to travel to the past and do what he does, watching for the killer so he can identify him.  Unfortunately it does not work.

Little more can be said without spoilers, and it will be difficult to follow the series without having seen the film, so now would be the time to stop reading and watch it if you intend to do so.  The film is marketed as a horror movie, and there are some gory scenes of murders and murder victims along with a couple of gratuitous sex scenes, so it is not for everyone.  It is, however, interesting and convoluted, and a lot of that is going to be unraveled quickly with major spoilers in the next paragraph.

The problems Sam encounters when he attempts to discover Rebecca's killer arise because the killer is also a time traveler, and one with intimate knowledge of Sam's intentions:  his sister Jenna.  This also complicates our analysis, because we do not know when Jenna makes her trips, or what trips she has made.

We can, though, conclude that she was very young when she made the first one.  She is a few years younger than Sam, and most probably made a short trip to the past to kill Rebecca.  To reach that conclusion you have to understand Jenna, though, and that involves the fire.

In the original history, Jenna died in the fire, but Sam and his parents escaped the burning house.  Sam cannot live with that outcome, so sometime shortly after the funeral he travels to the date of the fire, gets a ladder ready, and when the house is burning he climbs to the second floor window and rescues his sister, carrying her down the ladder.  He having saved her life, she is completely devoted to him.

We could say that no girl was good enough for Sam except Jenna, in Jenna's opinion; and she wanted her brother to be solely hers.  But what mattered with Rebecca wasn't that she was taking Sam away from her, but that she was cheating on him.  Eventually Rebecca must have told Sam, breaking his perhaps eighteen year old heart (Elizabeth is the younger sister, and is driving at the time of the murder, but they are all in high school).  Jenna kills Rebecca before this revelation, but would not have done so too long after the fact--people recover from high school breakups, and it is evident that Sam and Rebecca did not stay together (when Sam has undone all the deaths, he is married not to Rebecca, who is present at the party, but to Elizabeth).  The infidelitous Rebecca must die, in Jenna's view, for the hurt she caused her beautiful Sam.  So she makes a brief hop to the past, kills Rebecca in her own bed, setting it up for a time when she knew Lonnie was coming over and then framing him for the murder.

This is exactly the sort of paradox that makes the Butterfly Effect franchise so difficult, as the rules keep shifting and the viewer is never told how.  Both the fire and the murder give us anomalies that result in impossibilities, effectively grandfather paradoxes on a smaller scale, in which what the time traveler does prevents what the time traveler does.

Sam goes back to rescue Jenna from the fire because Jenna died in the fire.  Under fixed time theory this is not possible; there are several other reasons why fixed time would not work for this film, but this is sufficient to eliminate a fixed time explanation.  Under replacement theory we have an infinity loop:  Sam knows that Jenna died in the fire, so he makes a trip to the past and saves her from the fire, but now he does not know that she died in the fire so he does not make the trip (or travels to the past to save his parents instead), so she dies, and he makes the trip to save her, each history causing the other.

The question, though, is whether some version of multiple dimension theory will resolve it.  We thus have Sam leave from sometime after the funeral to the date of the fire, either entering or creating a new universe, and then returning to the future in the world he has defined by that act.

We now face the problem of the two Sams.  Even were we to suppose that it was only a week between the fire and the funeral, that's a week in which someone is living Sam Reid's life, building the memories of that first week after his parents died in the fire but somehow he saved his sister.  Then suddenly Sam, having leapt in and taken over his body during the fire, does so again, and all memory of that week is lost to him.  What happened to the Sam who lived through that week?

Ordinarily in such a case we would answer that there are now two Sams in this universe, the one who lived here all his life and the one who entered it from another universe and changed it.  But Sam travels by leaping into his own body, and so there is only one Sam because there is only one body.  What has become of the man who was Sam in this universe yesterday?  Where are the memories of the life he lived?

Further, if we accept that Sam has left his old universe, what becomes of him in that other universe--or, in later instances, of Jenna, his sister, who has to report that her brother died in her bathtub, in a tub filled with ice water while attached to the leads of a cardiac and encephalic monitoring system?  Either some version of Sam returns to his body, or his body is dead.  If the version that changed history does so, then he is in a universe he tried and failed to alter and presumably not also in the altered universe.  If the version of him he replaced does so, then he is disoriented, with no clear notion of how the world changed.  He might even travel back to the past to see if he can understand it; he might want to take his old life back from the version of himself who stole it from him.

These are persistent problems throughout the film; Sam always remembers the history he has undone, never the history he created.  Multiple dimension theory turns a disaster into an apocalypse.

There is a confusing aspect of Sam Reid's trips for those of us familiar with the prequels.  In the first film, Evan Treborn jumped into himself mostly in times when he had experienced blackouts, and discovered what had been happening around him that he could not remember, or changed it to suit what he needed.  He also went to one place he did remember, and twice to places he had previously visited.  His successer Nick Larson in the second entry does not have the blackouts, but takes over his body in places where it was.  With Sam, it seems he is able to arrange to have his younger body meet him at the address he specifies.

This is not clearly indicated.  However, it seems that he arrives not where his younger self happened to be at that moment but where he needs to be in order to witness events that are about to unfold.  It almost seems he is projecting a new body (on the order of Jack Starks in The Jacket), but that in the last trip we see him split between his future self and his past self after he does what he, his future self, intended to do.  So the film's conceit is still that he travels back to become himself in the past, but suddenly he is able to have that younger self at the scene of the crime.

How does this happen?  Does Sam actually enter his younger self wherever that younger self is, and then try to find a way to get to the scene of the crime to observe?  Or does his apparently psychic ability to time travel enable him first to tell that younger self to move to the specified location so that he can take over in time to do what needs to be done and exit?  Or does the younger Sam simply dematerialize wherever he was and rematerialize at the scene--and if so, does that reverse itself when he returns to the future, such that the younger Sam transports back?  The improbability is underscored when a young white Sam, grade school age, shows up somewhere in Detroit at the neighborhood Sweet Sixteen party of black Tiny Gasco to hear the first words Detective Glenn's wife ever said to him.  That raises a lot more questions, and a lot more problems.  The fact is, it is not merely improbable that the younger Sam was anywhere near these murders when they originally occurred; it is probably impossible, as then he would have been a witness to at least one of them before he made the trip, and probably a person of interest in a few in which he was seen near the scene.  That version of him would not be hiding, not expecting a murder to occur.  That he was always near these murders but never involved in the investigations is impossibly complicated--as the murder of Elizabeth will demonstrate.

We would have to say that it is at least inconsistent with the previous films in this regard.  Sam may be leaping into his past selves, but he is in the process also moving them to places they never would have been.  Neither Evan nor Nick ever did anything like that.

Following the fire we have at least twenty-three "safe" trips:  the one we observe in the opening moments of the film, and the twenty-two previous ones from which Sam was able positively to identify the perpetrators of other murders.  There might be others, trips he made to attempt to gain information in which he was unable to observe the criminal, which were also "safe".  By "safe" we mean that he made every effort not to interfere with events, or to be seen by anyone, in essence to be as little a part of the past which he was observing as possible.  But it is here that the film most fails to live up to its name.

"Butterfly effect" is a reference to a very small change triggering very large changes.  In terms of time travel stories, it means that the one little thing you do change in the past may well have serious consequences to the form of the future to which you return.  We see that in the later trips, as he does not understand why his life is worse with each return.  We accept that on the earlier trips he was safe, because he was not changing his own history.

But was he?

It is now the case that the young Sam Reid was present at or near the scenes of twenty-three murders--near enough to witness the crime and get a clear view of the perpetrator.  The film never explains the cognitive state of that other Sam, whether he experiences blackouts like Evan Treborn, or perhaps remembers the original history that has been unmade, or perhaps shares consciousness with his future self and so is aware of the events he is watching and why he is viewing these.  Never is he called as a witness, never is there any forensic or other evidence placing him at the scene.  We do not know how he gets to these locations, whether he is seen in transit, or whether he remembers having been there.  There is a great amount of uncertainty in the situation, and it would be very simple for suspicion to fall on him for any one or even several of these murders.

That is apart from the fact that he could have been seen by the murderer, and murdered himself, or threatened to keep silent.

It is also separate from the issue of what he would have been doing at the time.  Evan Treborn generally returned to moments in his past which he could not remember, and discovered what happened at those times; Nick Larsen changed events in his past, but not where he was at the time.  Sam Reid is removing himself from whatever he had been doing, and placing himself somewhere else.  Do those he was with miss him, notice his disappearance?  Does he leave something undone?  Does he always know where he went and how to get back, or is he sometimes lost in an unfamiliar neighborhood?

These are serious issues.  We do not know how much the police pay him for his psychic tips, but it is not so much that twenty-two checks in ten years will pay for his apartment, wherever it is, and help support his sister in her own place, as he apparently does.  It is possible that he is also hired by people, as Elizabeth suggests, to solve the murders of their loved ones, or that he becomes involved when substantial private rewards have been offered; and by others to discover other secrets, but we are never told that he does so--and the more trips he makes to the past, the more complicated his past life becomes.  Even now, he could not know whether at any moment a future version of himself might take over his body to go witness a murder, interrupting whatever he was doing.  His interruptions of his own life in the past mean that he is changing his own history by moving himself away from wherever he was to the scenes of these crimes.  The potential for butterfly effect changes is incredible; yet they never happen.

It is, of course, entirely possible that he managed to make all of these trips safely, changing nothing of consequence and having no impact on his own past life.  We do not condemn a time travel movie because it might have gone wrong but didn't; we assume that if it believes nothing went wrong then nothing went wrong, no matter how improbable that outcome might be.  We just wanted to put it on the record that this is terribly improbable, and embarrasing for a film that names itself after the very problem that ought to have been implicated here.

Things start to get very complicated as we approach the first murder, but there is a butterfly effect aspect to some of it.

We begin with Rebecca cheating on Sam with Lonnie.  At some point, Jenna must learn this, and she probably learns it from Sam, so someone has to tell Sam.  It might have been Rebecca herself, or it might have been Lonnie.  Elizabeth obviously fancies Sam, so perhaps she divulged her sister's secret in an effort to win him to herself.  However it happened, Sam is heartbroken, and perhaps like many teenagers in similar situations believes his life has come to an end.  However seriously he took it, Jenna saw that it was serious.

Jenna only needs to find a night on which Lonnie is expected to visit Rebecca at her house, and there was such a night when Rebecca had let both Sam and Lonnie know that her parents were not going to be home.  All she has to do then is surprise Rebecca, kill her, and escape so that Lonnie will blunder into the scene; she can thicken the plot by planting the murder weapon in his car or near his home, and if she covers the body she increases the chance that he will uncover it before he realizes she is dead, getting blood on himself.  In any case, it works:  Rebecca is dead, Lonnie is convicted, and Sam never learns that the girl he was seeing was cheating on him.  He also never connects with Elizabeth, as the entire incident is too painful.  Since Sam is unaware either that Jenna can time travel or that she is so enamored with him, and the police are quickly persuaded they have the right killer, he never wonders whether Lonnie might be innocent--until Elizabeth suggests it ten years later.

Now it gets messy.  Sam leaps back to the night of the crime, and we have a number of complications.  The first is, why did he not see the killer?  He knew the time of death from the police report, 12:40 A.M., and allowed time to reach the scene in advance, arriving at 12:20; she was already dead when he reached her.  Therefore Rebecca was killed earlier in this timeline than in the other.  That then means that, knowing that Sam was going to catch her, Jenna made another trip and moved the time of the murder back.  When, though, did she do this?

We might suppose Sam made the trip back, and then after he made his trip she made hers.  However, Sam remembers the events he sees, even after they have been changed, which means he would have seen her at the scene and returned to the future knowing it was her.  It is not at all clear that he would forget it when she changed events, as it was something he saw in the past, not something in his present.  So we might suppose she made her trip first--but that won't work either, because he is relying on a police report of which he has a copy, and if the time of death changed in the real world before he departed, it would have been different in the police report when he made his final preparations.  So the only possibility is that at the very same instant that Sam makes his trip to the past, Jenna makes hers.

The idea that two people independently leave the present by different means at the same instant is not really plausible, but it could happen, and we're a bit fuzzy on the details of how long an "instant" would be in this case.  She knows when Sam is leaving because she is monitoring him; she apparently has more control over her gift perhaps than he has over his, as she takes none of his precautions and he never catches her doing it.  Therefore she leaps from the same instant in the future, arriving perhaps an hour earlier in the past, kills Rebecca ahead of schedule, and slips out to make sure things go correctly.

Why, though, does she kill Elizabeth?

We might conclude, based on the ending (in which Sam and Elizabeth are married), that Jenna wants to nip that relationship in the bud because she knows they will connect.  Yet she cannot know that at this point, because they did not connect either when Rebecca lived or when only Rebecca died.  The real problem here for Jenna is that Elizabeth has seen Sam enter the house, and will tell the police, who will close in on him--and meanwhile, Lonnie also saw Sam in the driveway with Elizabeth, and did not enter the house, so he did not find the body and was cleared in the investigation.  Sam is now a "person of interest" in the case, and the frame of Lonnie has fallen apart.  However, had Elizabeth lived to tell what she knew, Sam would have been convicted.  Jenna is protecting Sam at this point.

There are some other peculiar results as well, at the other end of our timeline.  Sam is now unknown to the police except as a "former suspect" in an unsolved double homicide that is now attributed to a serial killer, the "Pontiac Killer", who has been killing about one person per year since then.  This Sam has never used his gift to identify a killer, apparently, but since he was a suspect in the first killings and has since been fixated on the case, they let him look at the files related to all the killings.

Meanwhile, apparently the loss of the income from solving cases has led to the need to rent his couch to Paco, someone he never knew in the other history.  We never learn what his regular income source is, whether he has a job or lives off the life and fire insurance from the accident, but somehow now he has a shortage.  Since we do not know the source of his money apart from the police jobs, we cannot explain why it is now inadequate, other than that it must be the case that he works some other job we never see.  That becomes clearer with the next trip.

What is more peculiar now is that Sam is not using his gift to solve unsolved murders at all.  He is still close to Jenna; he still talks about how to use his ability with Goldburg.  Why would he not be using it as he was in the previous history?  It cannot be because the police would not listen; they listen to criminals all the time, and he was suspected but not charged with the first murders, so he could have been a psychic informer.  Perhaps more pointedly, why has he, that is, the Sam who lived in this timeline up to this moment and who does not know that his other self has already interfered in events, not attempted much sooner to solve the Brown case by traveling back to the scene and trying to observe the murderer?  Certainly Jenna would have attempted to prevent that--but now we have a barrage of Sams and Jennas coming from different points in various versions of history, the Sams attempting to recognize the killer and the Jennas attempting to avoid being recognized, but all of them doing so through the control of one Sam body and one Jenna body.  It would be a nightmare to unravel how that all happened.  Our problem, though, is why it didn't.

It is significant that Sam received Rebecca's diary in 2008 from Elizabeth, who now died in 1998.  The effects are not undone.

Certainly these are "butterfly effect" problems, major changes from small differences in the past.  It may be that the change from being an early suspect in the murder of his girlfriend whose killer has been convicted to being an early suspect in an unsolved double murder of his girlfriend and her sister has interfered with his life in other ways.  It still is difficult to fathom why what he did has had the impact it has.  The other films did some things that did not make sense, but usually we could understand how what Evan or Nick did brought about the futures we saw.  Here no effort is made to explain this other than the general notion that whenever he travels to his own past he makes things worse generally as well as for himself.

There is another problem with the murders of Rebecca and Elizabeth Brown, but it is a problem not with Sam's trip but with Jenna's.  It is a sort of grandfather paradox variant which ought to lead to an infinity loop.  The problem is, having killed Rebecca and framed Lonnie, how does she know to kill Rebecca and frame Lonnie?

The problem would be easier to see were it not for the film's primary conceit, that she uses her earlier body.  Overlooking that, we have Jenna traveling to June 6th, 1998, killing Rebecca, framing Lonnie, and returning to the future.  We agreed that this was shortly after Sam discovered Rebecca was cheating on him, so we'll place it as July 6th, 1998.  Now on the morning of June 7th, the Browns and the Reids and the Flennons and everyone else are awakened to the knowledge that Rebecca was murdered.  The investigation begins, it touches Sam but catches Lonnie, and by July 7th everything is moving to a conclusion.  Rebecca is dead, Lonnie supposedly having killed her because she would not leave Sam for him.  Jenna has no reason to travel to the past to kill Rebecca.

But she already did, you say.  Perhaps relying on a doubtful interpretation of Niven's Law, you claim that whatever she did in the past has now been done.  That will not work, either.  There are a lot of reasons why this understanding of Niven's Law is faulty, and we will return to the problem before we are done; but if Jenna travels to the past and kills Rebecca, she prevents herself from knowing she should do it, and so prevents herself from traveling to the past to kill Rebecca.

This problem will repeat itself with each of Jenna's killings.  It is perhaps most notable with the next one, though, when Jenna kills, and then does not kill, Anita Barnes.

The murder of Anita Barnes gives us new problems.

The first is, when did Jenna do this?  Not when was the murder committed--we know that:  it happened on September 5th, 2000.  We also know that it happened before Sam ever met Anita, because Jenna knew that after they met they would enter a relationship which she could not allow.  That means that the relationship had begun, and gotten serious enough that it concerned Jenna.  She needed only give herself a few days lead time before they met, as long as she could be certain of when that was, so he probably met her in mid September.  Since he can see no connection to her when he investigates her death, it won't have been something predictable, so it might take a few weeks before the relationship was serious.  So perhaps a month or two after the date of the murder Jenna leaves the future to eliminate her rival for Sam's affection.

That, though, means it's not the 2008 Jenna who makes the trip; it's the 2000 Jenna who does so.  But the 2008 Jenna remembers having made the trip in 2000, even though in the original history before Sam left for Rebecca Jenna had not killed anyone other than Rebecca.  Jenna also made a trip at that time, and killed Elizabeth; but now in the intervening years, the years of which Sam cannot remember the real history only the previous history before it was changed, Jenna has made a trip to the past and killed Anita because she was going to connect with Sam, and Jenna remembers having done so and why.

The information problem is also clearly in play here, as once Jenna kills Anita, Anita never becomes a problem, and Jenna has no reason to kill her.

Sam hides in the closet when Anita surprises him, and then witnesses what looks as if it is going to be a rape but is actually rough sex she wanted her boyfriend to try.  He is found, and Anita throws him out and obtains a restraining order against him--but she is never murdered.  Of course, now it is not necessary for Jenna to murder Anita, because Sam has ruined any chance he might have had with her, and it would be easy to assume that therefore 2000 Jenna having no reason to travel back does not do so, and does not appear in the past.  Yet this is the same problem which in every other instance is resolved by reliance on Niven's Law, in essence that once the past has been changed it remains changed without the time traveler leaving the future to do so, unless changed by some other interference.  There is no reason that 2008 Sam hiding in the closet should prevent 2000 Jenna from killing Anita, any more than that Anita's death would prevent itself.

To be consistent with the other trips, 2008 Jenna, aware that 2008 Sam is likely to catch her, must leap back and seize control of herself from herself, preventing herself from committing the murder.  Again we have to have her making her trip simultaneously with his, again against the odds.  Jenna is not monitoring him this time.  She tried to dissuade him from making the trip.  That she would make her trip at the same instant without observing him seems too incredible.  Yet either that is what happened, or she was surreptitiously watching him.  The latter is plausible enough, and we are uninformed concerning her movements, so it is possible that she stalks him, realizes what he is doing and how that would ruin things, and manages to jump to the past at the moment she sees his bathroom light extinguished.  Thus it works, if we accept this one difficulty.

It is still uncertain, as she cannot know that Sam's presence in that apartment would derail their future relationship--it is a poor way to meet someone, like bumping your car into the pretty girl's car so you can get her name and address from her driver's license--but they did meet, and they could still build a relationship.  Thus the question of why Anita Barnes did not die plagues the film, because once Jenna kills her Jenna must consciously choose not to kill her, and prevent the murder, without knowing what happens if she lives.

We find the issue fascinating, wondering with Sam what changed, but at this point the film is cheating us, changing the rules so that what would be impossible elsewhere in the story is what happens here.  The franchise has done this kind of thing before, posing puzzles that have no real answers, and it is a problem with the entire series, that nothing in the time travel is consistent or well-considered.

The problems with the Anita Barnes murder are also the tip of another iceberg, because according to police records she is the third victim of eight, Rebecca and Elizabeth being the first two.  It is a bit vague, as police say they happen about one year apart, and we know the first two occurred together in 1998, the second in 2000, and so we have 2001 through 2008 to fill with only five murders (it is midway through 2008 at this point).  The math says that if they were evenly spaced running to the present, they would fall roughly every eighteen months.  That is of no consequence, it just makes it more difficult to talk about the murders individually.

As an incidental, there is some problem about the number being so low.  We understand that Sam might have had a serious relationship start and not go anywhere every year or two; but the problem is that he does not, that all of these murders represent relationships that never started.  He does not connect with Anita Barnes because he never meets her; does he really meet no one else in the next year who is interested in him?  Remember, it is not that he took an interest in a girl and then she died; it's that the girl died before he ever met her.  Might he not have met anyone else, or wondered why over the course of a decade he had no serious relationships?  But it's just odd, not impossible.

The bigger problem is that Jenna has been very busy in this altered history.  While Sam was visiting Rebecca, Jenna was killing Elizabeth--perfectly reasonable, as a witness who could place Sam in the house.  Then, before Sam can return to the future, Jenna sees all of his relationships between 1998 and 2008, and kills all the girls before he meets them.  That is, in 2000 Sam starts seeing Anita, and Jenna goes back to before they met and kills her.  Then, perhaps in the spring of 2002, Sam starts seeing someone else, someone he would never have met had his relationship with Anita gone as well as Jenna feared, and Jenna again travels back to kill her.  The fall of 2003 is Sam's next tryst, again which would not have happened had Jenna not prevented the 2002 tryst, and we have another in the spring of 2005 which would not have happened without the earlier murders.  Sam is oblivious to all this; the day before he went back to try to identify Rebecca's killer there was only the one murder, and the day he returned it was the work of a serial killer.  Jenna, however, is conscious of having lived through the altered histories, the one Sam (and Nick and Evan) never remembers.  Jenna's experience is different--but if so, how does she remember both the history from which she went to the past and the history that she created?

Sam does not have such memories; he does not understand why his situation is worsening, as he goes from not owning a car to renting space on someone's couch to living with his sister, from reasonably respected psychic working for the police to arrested suspected serial killer.  Her ability is different in kind from his, but we never get the details.

There is a clue to the killer that inexplicably escapes Sam's notice.  That's not to say he does not recognize the fact; he fails rather to recognize its significance.

When Sam returns from his failed attempt to catch Rebecca's killer, in which Elizabeth is also killed, he finds that they are now the first two of eight killings attributed to the "Pontiac Killer".  He discusses the problem with Professor Goldburg, and the suggestion throughout is that he knows none of these victims.  He also goes to confront Lonnie Flennons, now not a convicted murderer on death row but a reasonably successful lawyer and paraplegic due to an accident five years before.  What matters is that Lonnie is alive, and not on the list.

Then Sam goes back to observe Anita Barnes' murder, and when he returns Anita has not been murdered--but Lonnie has.  It is mentioned twice, once by Detective Nicholas who says that Sam saw Flennons the day before he died, and once by Sam when he corrects himself that it was not eight women (which it was when Anita was included) but seven women plus Lonnie (still eight victims).  Sam wonders why Anita is alive; but he fails to wonder why Lonnie is dead.  All things being equal, we would assume Sam visited Lonnie on June 6th, 2003 (as Lonnie mentions that during the 2008 visit at the law office), and Lonnie was killed the next day.

This oversight is the more peculiar because Lonnie breaks the pattern in two ways.  First, he is the only man that the killer targets, as far as the police know (the killer also kills Professor Goldburg, but his body is never found so he is listed as "missing").  Second, he is the only person on the list whom Sam knows.  Given those details and the fact that when Anita dropped from the list Lonnie was suddenly added to it, Sam ought to have recognized the anomaly and asked questions about it.  Yet he never seems to wonder why his mystery killer kills this one man, and only after (in metaphysical terms) he does not kill Barnes.

It probably would not get him to the truth.  Sam is oblivious to the fact that Jenna also travels in time, and it makes some sense for someone with what seems to be a unique ability to assume that it is.  Although we might hypothesize that someone else with the same time travel ability might be changing the past, it is the kind of hypothesis that would be ignored even by someone who has that ability.  It just seems too improbable.  Yet the fact that he probably will not find the answer does not mean he should not be asking the questions.

Besides, Goldberg apparently was figuring it out--although Jenna claimed that he was going to give evidence against Sam, she ultimately admitted that he had figured out her involvement.  So perhaps if Sam had focused more on the one victim he knew, he might have worked out the connection.

We have another victim who breaks the pattern--in some of the same ways that Lonnie Flennons did, but in some peculiar ways as well.  The barmaid Vicki is rather gruesomely killed shortly after Sam leaves the bar.

Part of the problem is that this murder happens in what is for Sam the present; but Jenna always attacks from the future.  This suggests that at some point in the future Jenna had a reason to eliminate Vicki.  That, though, is also problematic.  In the history in which Rebecca is the only victim, Vicki went home with Sam for an ill-fated tryst (his mind was occupied by the death of Rebecca at the time), but after Elizabeth is killed that goes in the category of "never happened".  Sam even makes oblique reference to something happening in another life, but at this point Vicki is engaged and not cheating, so even though it may be good business sense to flirt with customers for better tips, she's drawn a line and sees no future with Sam.

It is problematic for Jenna in another way:  it obviously implicates Sam.  In every other case, she targeted girls Sam had not yet met, that is, traveled to a time before he knew them.  He has known Vicki for at least a little while, maybe a few years, coming into her bar with or without Goldburg.  Yet Jenna could have targeted her years before, preventing her from having taken the job at the bar.  She could have done so weeks before, prior to the night Sam brought her home.  If her interest is to protect Sam, she certainly could have picked a better time than minutes after he left the girl alone in the bar.

We must assume that Vicki's engagement sours.  Whether they break up or just have a bad fight, she remembers chatting with Sam and decides to see if he is still interested.  This time the relationship must work.  We must suppose it is at least a few weeks, perhaps a few months, in the future, and it looks like the relationship is progressing.  Jenna decides to nip it in the bud, remembers that Vicki was engaged and thinks she can frame a jealous fiance for the killing--perhaps overlooking the fact that the method of the murder is going to point to the serial killer and away from any individual candidate.  She perhaps does not realize that Sam was there that night, at least until it is too late; or perhaps Sam is there most nights, and she simply does not realize he was the last customer that time.  So she makes her leap back, kills the girl, and then returns to her own time, leaving her younger self to deal with the consequences.

The alternative is that Jenna has become so jealously protective of Sam that she watched him at the bar, saw his flirting rebuffed, and took action immediately.  That is very unlike her, and very dangerous, as she does not have the advantages of leaping in from the future with a well-considered plan.

Thus we also have the odd suggestion that there was already a future in which Vicki was not killed, Sam not arrested for her murder, and an entirely different set of events unfolded.  Perhaps Sam figured out that Jenna did it, and Jenna decided to eliminate Vicki as a way of moving suspicion onto Sam, to attempt to control him.  However we parse it, though, it does not fit the pattern well at all.

At one point, Professor Goldburg warns Sam against doing it, saying he will certainly fry his brain if he tries.  But then, it is obvious to us that Jenna has done it, and in the other films we saw Nick do it once and Evan do it multiple times, and Sam is in a desperate situation at the moment so he has to do something.  He leaps back to take control of himself in a time in which he had previously leapt back and taken control of himself.

O.K., so he did not fry his brain.  He still raised issues we still cannot resolve.  In short, if Sam leaps into himself in what we take to be about 1995 from later in 1995 intending to save Jenna from the flames, and then in 2008 leaps into himself in that same moment back in 1995 intending to prevent her from escaping from the fire, which version of him controls his body?  After all, even though Sam can assure the death of Jenna in 1995 (and he does more than is necessary, since he already knows that if he does not help her she will die in the fire, so all he has to do is not help her) he cannot thereby prevent himself from making the short leap back from 1995 to 1995 to save her, and he is now caught between saving her and killing her.  It is not even as if he has undone the version of himself that originally saved her.  That version of himself in theory undid himself when he eliminated his reason for saving her by doing so.  Now as he causes her to die in the fire, he recreates the version of himself who chose to go back to save her.

On the other hand, his options are limited.  He cannot go back and prevent himself from going back, because when he went back before he already did prevent himself from going back--for whatever reason, preventing someone from traveling to the past to change something does not undo the change.  That version of himself ceased to exist when Jenna lived.  The best he can do to prevent himself from saving her is leap into that situation and take control so that Jenna dies--but that recreates the version of himself who saves her, so he would also have to figure out how to prevent himself from going back to save her.

The film gives no good answers to these issues; and these issues raise another set.

We wrote,

for whatever reason, preventing someone from traveling to the past to change something does not undo the change.

That is consistently so throughout the movie.  When Jenna kills Rebecca she effectively prevents herself from killing Rebecca; then again when she kills Elizabeth, and with each of her other killings.  The victims remain dead, even though now there is no reason for them to have been killed.  The causal chain has been broken, but perhaps because of Niven's Law the past remains in its altered form.

So we have established that you cannot undo changes in the past by preventing the time traveler from making them; once they have been made, they are there.

Yet at the end, this fundamental rule of how time travel works is absolutely violated as Sam kills Jenna, trapping her in her room during the fire so that she cannot escape.  This means that Jenna will never travel to any point in the past and kill anyone, because she died before she did so.  Yet that solution is exactly opposite to the solution in every other case.

Oh, but this is different.  Is it?

With Rebecca's murder, Jenna made only a short trip, from 1998 to 1998.  Then, a decade later in 2008, she came back again and killed Elizabeth also, also in 1998.  But between 1998 and 2008 she made several other trips.  From Jenna's perspective, she actually killed Anita Barnes before she killed Elizabeth, because she made a short trip from late 2000 back to September to eliminate her before she met Sam; she did not go back to kill Elizabeth until 2008, even though she killed her in 1998.  Similarly, she killed Lonnie Flennons on a short hop back from the fall to June 2003, long before she went back to kill Elizabeth.  Let us imagine, though, that when she leaves 2008 to kill Elizabeth something goes wrong, and she is killed fleeing the scene.  Who dies?  Her 2008 self who is in control has already killed several people in the future.  We can argue that since her 1998 self dies, her 2000 and 2003 selves never make their trips; but in that case, her 2008 self will never make her trip, either, and Jenna will not be killed fleeing the scene of the crime because she will not have gone back to kill Elizabeth.  Yet if Jenna's arrival from 2008 is maintained despite her death in 1998, would that not mean that all of the consequences of her trips would be retained?  She has no body into which to leap, but apparently that is not needed--if you do not need to make the trip back in the altered timeline to retain the consequences of your actions in the past, you do not need to be there to do so.  Anita Barnes and Lonnie Flennons are still gruesomely murdered, and the killer apparently was never there.

The story is much more complicated than we see.  At the birthday party Professor Goldberg comments about being eager to hear the new stories, and so this version of Sam obviously has been using his ability and confiding in the professor, who obviously does not remember any of the other histories.  We have no idea what impact any of those trips made, nor indeed any trips by any of the other Sams (or Jennas) in any of the many altered histories.  We only know that they happened.

As a time travel movie, it maintains the inconsistencies of its predecessors.  It has a clever twist as a murder mystery, and I admit I did not see the solution coming; but nothing in the time travel makes sense on its own, and it contradicts its own rules more than once.

It may be that one aspect of this analysis has not been clear, regarding what Sam does and does not remember.  The complication arises because we have two time travelers.

When Sam changes the past and returns to the future, he remembers the past that was, through which he lived before his trip, but he arrives in the past he created.  Everyone else in the world remembers only the past he created, not the past which was undone.

We assume that also applies to Jenna, in both directions:  if Sam travels to the past, she does not remember the history he undid but that which he created, and if Jenna travels to the past, Sam does not remember the history she undid, but Jenna does not remember the history she created.  She even comments on one occasion to the effect that she has already told him something multiple times, which he does not remember.  Of course, we have reason to suspect that Jenna's gift is stronger than Sam's, but at least we are justified in assuming that when Jenna uses her gift Sam has the same experience as everyone else, of remembering history the way she made it.  That is what happened when Jenna killed Rebecca; Sam had no recollection of a history in which Rebecca was not murdered and Lonnie not arrested.  Then of course we have the history in which Sam travels back to see who killed Rebecca, and Jenna also travels back to kill Elizabeth.  We can accept that this time Sam does not remember the new history because he was in the past with Jenna when she made those changes.

However, as we move forward, we know that in this altered history Jenna kills several more people.  When it appears that Sam is building a relationship with Anita, Jenna travels to the past to kill her.  She does the same for several other people with whom Sam has a relationship, and Sam never remembers having had a relationship with any of them, so in that sense he is not remembering the original past.  The problem is, Sam does not remember the history between the death of Elizabeth and the death of Anita.  If by traveling to the past, Jenna has reset everyone's memories to the events which come from her trip to the past, then when she killed Anita that ought to have reset Sam's memories to the new timeline.  He was not in the past at that moment--we only think he was, because he leapt over the intervening decade, but there was a version of him that lived through those times and events, who was alive to start dating Anita, alive when Jenna left for the past to kill her, and alive when Anita was murdered.  Of course he forgets dating Anita, because that history has been undone; but it was the undoing of the history that he knew following the double-murders of Rebecca and Elizabeth, which is the history he ought to remember.  We see the same problem when Jenna kills Lonnie, that Sam remembers visiting Lonnie just the other day, although Lonnie died five years ago, victim not of Sam's time travel but Jenna's.  If Jenna erased the history in which Sam visited Lonnie, and Sam cannot remember the histories Jenna has erased (such as the one in which Rebecca was not killed and Sam ultimately learned of her infidelity), then Sam should not be able to remember having met with Lonnie, who was dead before Sam visited him.

The film is again inconsistent, not giving enough thought to what the time travelers are able and unable to recall.  It has the makings of a decent time travel murder mystery, but breaks too many of its own rules along the way.