The movie starts with a medical patient, played by Ashton Kutcher, breaking into a doctor's office at night. The noise has alerted some guards, and he can hear them looking for him. He blocks the door with a couch, hurriedly grabs a pencil and paper and starts writing "If someone reads this, it means that I was unsuccessful and am already dead..." The guards are now outside the office, their flashlights shining in as the scene fades out.
The movie then goes back to "thirteen years earlier". We meet the young 8 year old Evan Treborn (the adult is played by Ashton Kutcher) who is being raised alone by his mother, a nurse. When he is dropped off at school, Evan's teacher insists on speaking with his mother on an urgent matter. Apparently, as part of a drawing assignment, Evan drew a very disturbing picture of himself holding a knife over a couple of dead bodies. Evan has also started experiencing blackouts where he does not remember what has happened. We then follow Evan's life along with three of his friends, Kayleigh Miller (adult played by Amy Smart), her brother Tommy, and Lenny. The following four episodes are pivotal moments, which are referred to later in the movie. In each, we see that Evan has blacked out certain memories.
At 8 years old, Evan is dropped off at his friend Kayleigh's house. Her dad has just picked up a new video camera, and he wants to make a home movie with Kayleigh and Evan. At this point, Evan blacks out, and he finds himself naked with Kayleigh in the basement of the house. Mr. Miller has just finished making a movie, but Evan doesn't remember what has just happened.
Concerned about his blackouts, Evan's mother takes him to see a doctor at a psychiatric institution. The doctor notes that Evan's blackouts do not seem to have a physical cause, and hypothesizes that they may be stress related. He recommends that Evan keep a journal as treatment (important).
We find out that Evan's father is in a psychiatric institution, and that they have never met. Evan's doctor theorizes that his blackouts may also be related to him not having a father figure, and recommends that they meet in a controlled environment. They meet, but then Evan blacks out and awakens to see his father strangling him. The guards tear him off of Evan, beat him with a truncheon and kills him.
At 13 years old, we see Evan and his friends smoking and rummaging in the Millers' basement. Tommy finds a stick of dynamite, and they decide to use it for a prank. They light it and put it into a mailbox of a neighbor's house, and wait in the woods by the house for it to explode. Evan blacks out, and then he finds them all running in a panic through woods dragging Lenny with them, who appears to be catatonic but otherwise uninjured. Evan has no idea what has just happened, and Lenny has to go to the hospital for treatment.
The following scene does not involve a blackout, but provides context for what happens next. Evan, Kayleigh and Tommy go to see a movie. Tommy catches Kayleigh and Evan kissing and is enraged. He beats up another boy and you can see in his eyes that he loathes Evan.
Still at 13 years old, Lenny has come back from the hospital. Evan and Kayleigh go to visit Lenny, and together they wander into a junkyard, where they see some smoke. They happen upon Tommy, who has tied up Evan's dog in a bag, doused it with gasoline, and is preparing to light it on fire. Evan tries to stop Tommy, but Tommy picks up a stick and accidentally hits Kayleigh as he swings at Evan. Evan blacks out, and wakes up to find himself and Kayleigh bloodied, Lenny unhurt, and a charred bag with the remains of his dog.
At this point, Evan's mother has decided that they will move away. As their U-Haul truck is pulling away, Evan sees Kayleigh and writes a note to show her through the window: "I'll come back for you".
We go to present day, where the 20 year old Evan is a student at university studying psychology and memory in particular. His roommate Thumper is a punk-goth type, and gets along well with Evan the studious-grunge type.
They go out to celebrate after one of Evan's exams, the occasion being that he has not had a blackout in 7 years. They go to a bar where Evan picks up, and brings a chick back to his dorm. She finds his stash of journals which he apparently has kept all through the years. He's embarrassed about them, but on her request he begins reading a passage out of one of the journals. Something very strange when he reads a part that approaches one of his blackouts as a kid. He's reading the part in Episode 4, and all of a sudden he's thrown back to that instance, but evidently with his adult memory intact. He finally sees what he had blacked out all these years.
Evan is hit by Tommy with the stick and can't save his dog. Lenny is trying to untie the rope around the bag, but when Tommy notices this he threatens him by saying he'll kill his mother in her sleep. Lenny backs off, and Tommy lights the bag. Evan then wakes up in present time to find that he has blacked out momentarily.
Evan is not sure whether this is a real memory, so he goes to visit Lenny. The adult Lenny is a very introverted and somewhat disturbed individual. Evan asks whether he remembers the time that they found Tommy in the junkyard. Lenny barks out what Tommy had said "If you do anything, I'll kill your mother in her sleep!"
Evan realizes that reading the entry leading up to a blackout, he can go back in time to that moment. Intrigued, he reads another passage in one of his journals leading up to Episode 3 above. He is thrown back to the him and his friends waiting for the mailbox to explode. Lost in the moment, the cigarette falls out of his mouth (which did not happen in the original Episode 3) and onto his shirt, burning him. A car pulls into the driveway of the house, and a mother and baby get out. Before heading inside, the mother decides to pick up the mail. The four watch in horror as the mother and child go to the mailbox and it explodes. While Evan, Kayleigh and Tommy run from the scene, Lenny is totally stunned and traumatized and has to be dragged away from the scene.
Back in present time, Evan finds that he has a new scar from the cigarette burn that he didn't have before. From this, it appears that what happens in the past can happen differently, depending on his actions. However, he is hesitant to continue investigating where his repressed memories may lead. He goes back to visit Kayleigh, who he apparently has not seen since he moved away at 13. After she leaves her job working in a diner, he meets her and starts questioning her about the past. Kayleigh reveals that when her parents split up, she had a choice to live with her father, or with her mother who lived out of town. As they were childhood friends, she chose to live with her father as she didn't want to move away (important later). Evan then starts asking her about the time they made a movie with her father (a memory he has not revisited yet). She gets very upset, and he realizes that they were abused and forced to do a kiddie porn film, and she leaves him crying.
When Evan gets back to his dorm, he receives a message and learns that Kayleigh has killed herself. At this point he makes the active decision to go change the past. He reads the journal passage bringing him back to Episode 1 above. Kayleigh and Evan are in the Mr. Miller's basement with costumes on, the video camera is running. Mr. Miller instructs them to take off their clothes, but then Evan challenges Miller in an adult tone, saying that what he is doing will ruin his daughter's life and lead to her suicide. He adds that he should raise his daughter lovingly, and adds that he should discipline his son Tommy, as he is a sick person. In a hard to believe development, this seems to convince Miller, who seems genuinely contrite and promises to change his ways.
Evan wakes up in present time to find himself in bed with Kayleigh. He then has new memories flooding back into him, as he has changed how everything developed because of that one instance (sort of like Rufus Sewell in Dark City getting his past reprogrammed). Kayleigh grew up not being abused by her father, and snuck away to meet him when he moved away. They started dating, and are now in college together. She is in a sorority, and in a humorous development, he is a stereotypical frat boy.
We see that his relationships are totally different, for example he runs into his roommate Thumper from the original timeline, who understandably as a punk-goth type has nothing to do with frat boy Evan. But By the way, for the plot to work, Evan also retains all of his old memories of the alternate timeline.
Life seems perfect for Evan as he is with Kayleigh, but we soon see the negative ramifications of his actions. Although Kayleigh grew up fine, Tommy became the object of Mr. Miller's wrath growing up. A confrontation involving Evan, Tommy, and a baseball bat ensues, in which Evan kills Tommy. Evan is sent to prison, and he manages to get possession of one of his journals so that he can change the past again. He reads the passage leading up to Episode 4.
Evan, Kayleigh and Lenny are just about to come upon Tommy. Evan realizes that they have to be prepared this time in order to change the past, so he picks up a shard of metal and gives it to Lenny, telling him to use it to "cut the rope" (to free the his dog from the bag). However, during the confrontation with Tommy, he changes things himself, and convinces Tommy not to kill the dog. Just as Tommy puts down the stick, he is stabbed by Lenny with the metal shard and killed.
Evan then awakens in a very grim present drastically changed as a result of Tommy's death. Lenny is a permanently restrained patient in a psychiatric facility, and Kayleigh is a crack whore.
Evan realizes that he has to go back and change things once more. He goes back to Episode 2, and with the knowledge he now has, he speaks with his father about how he can change things. His father was institutionalized as he has the same "gift" that Evan has - and was diagnosed to be delusional. His father tells him that he can't play God, all this changing the past has to end here. Evan refuses and his father lunges at him, strangling him as the guards grab at him. (Note: this particular incident may be a bit out of order, I don't remember exactly where it was as it didn't really change the past)
Back in the present, Evan then decides to go back to the pivotal moment in Episode 3.
Instead of watching the inevitable explosion, Evan runs out and shouts at the mother to get away from the mailbox. As he gets to the mailbox, it explodes and he is thrown back.
Evan wakes up in the present, and finds that his roommate in college is apparently a very well-adjusted and social Lenny. The downside - Evan does not have any arms, as they were amputated due to the injuries from the explosion. Other things have changed as well, Kayleigh is Lenny's girlfriend, and Tommy is a religious-preppy type, and they are all still best friends. Though he feels sorry for himself, he sees that everybody else is happier. He tries to kill himself, but fails when Tommy saves him. He then visits his mother in the hospital, who is dying of lung cancer. Apparently, in this timeline his mother started smoking again as a result of the dynamite accident. This convinces him to try to change the past again.
He goes back to Episode 1, and tries to kill too many birds with one stone. He grabs a candle, and the finds the stick of dynamite that is also in the basement. He tries to threaten Mr. Miller into not harming anyone, but this backfires, and he drops the lit stick of dynamite which explodes when Kayleigh picks it up.
Evan returns to the present as an institutionalized psychiatric patient. The incident involving Kayleigh's death led to a string of events culminating in Evan's present condition. As everything is wrong, and Kayleigh is dead, he has to try to change the past again. He storms in to see his doctor, and demands his journals. However, the doctor says that there are no journals. Rather, all of his memories are a delusional fabrication he has concocted as a result of his guilt over his role in Kayleigh's death. In this timeline, the chain of events he set off have resulted in him not keeping any journals. The doctor then comments that this is the same affliction that befell his father, and in the end his father kept asking to see an old photo album that never existed. This provides a clue to Evan, that there are other ways to change the past.
The next time he is in the doctor's office, his mother is also there. He asks his mother the old home videos they did when he was a child. She promises to bring them. As he is leaving, he hears the doctor recommend that he be transferred to another hospital soon, so Evan realizes that he doesn't have much time left.
We see Evan sneaking around in the institution at night, breaking into the doctor's office (back to the very first scene of the movie). Barricaded in the office, as he finishes his note he starts playing a projector with one of his mother's old home videos. The guards are breaking into the office, but the film works and he is thrown back into the past, before any of Episodes 1-4.
There is a backyard party with the first meeting between the young Evan and young Kayleigh. As they meet, Evan very deliberately whispers into Kayleigh's ear: "I hate you and if you ever talk to me, I'll kill you and your family." She runs away from him crying.
Back in the present, he is with Lenny his roommate and asks "Where's Kayleigh?" to which Lenny replies "Who's Kayleigh?" Not suprisingly, they never became friends in this timeline. He goes back to the diner where Kayleigh was working in an earlier timeline, but she never worked there. Evidently she and her brother moved with their mother when their parents split up. Kayleigh, Tommy and Lenny have all turned out fine, given that none of Episodes 1-4 have happened. Although he is not with Kayleigh, this is one life that Evan can accept, and he burns the journals.
"Eight years later" - Evan is working in New York, talking on a cell phone with his mom. He passes by Kayleigh on the street who does a double take as she passes by him, he does the same a moment later but misses her glance. It appears that although they were never together in this timeline, there is still some connection between them.
NOTE: The ending of the Director's cut DVD ends this way.
Thanks to goldenerafan for submitting it.
After breaking into the doctor's office Evan begins watching films from a projector (from the beginning of the film); we then seen Evan's mother in the delivery room. We hear her telling Evan, in an overvoice, about her losing previous babies, and he being her miracle child (this from earlier in the film, after Evan and his mother visit a psychic who, spooked from not finding Evan's lifeline, tells him he was never supposed to be born.)
In the womb, the unborn Evan begins choking himself with his umbilical cord - he slowly begins to die. After he dies we see his mother crying in her hospital room.