The Butterfly Effect

Plot

Evan Treborn (Ashton Kutcher), who suffered severe traumas as a boy (played by Logan Lerman) and a teenager (played by John Patrick Amedori), blacks out frequently, often at moments of high stress. While entertaining a girl in his dorm room, he finds that when he reads from his adolescent journals, he travels back in time, and he is able to basically "redo" parts of his past, thereby causing the blackouts he experienced as a child. There are consequences to his choices, however, that then propagate back to his present life: his alternate futures vary from college student, to prisoner, to amputee. His efforts are driven by the desire to undo the most unpleasant events of his childhood which coincide with his mysterious blackouts, including saving his childhood sweetheart Kayleigh (Amy Smart) from being molested by her father (Eric Stoltz) and harassed by her aggressive brother (William Lee Scott).

The actions he takes, and those he enables others to take during his blackouts, change the timeline in the new future wherein he awakes. As he continues to do this he realizes that even though his intentions are good his actions have unforeseen consequences. Moreover, the assimilation of dozens of years' worth of new memories from the alternate timelines causes him brain damage and severe nosebleeds. Ultimately, he decides that his attempts to alter the past end up only harming those he cares about. But the focal point for all of these traumatic timelines appears to be Kayleigh, so Evan travels back in time once more to the first day he met her and by scaring her away finally succeeds in saving Kayleigh's life. He then destroys all of his journals so that he's not ever tempted again to make any more changes.

The film ends eight years in the future with Evan leaving an office building in Manhattan and passing Kayleigh on a crowded daytime sidewalk. They alternately pause and turn after spotting and passing each other. While Kayleigh seems to have only a vague intimation of having seen him somewhere before, Evan remembers her very well and allows the moment to pass without attempting to speak to her.