From an early age, Evan Treborn (Ashton Kutcher) has lost track of time, crucial moments in his life have fallen into oblivion. What remains is the ghost of memory and the broken lifes around him, those of his childhood friends, Kayleigh (Amy Smart), Lenny (Elden Henson) and Tommy (William Lee Scott).
Aided by a psychologist, Evan wrote a diary during his childhood. Later, in college, decides to read one of his diaries, and suddenly and inexplicably he found in the past. Finally you realize that diaries are a vehicle to go back to past and retrieve their memories. However, these memories only make feel at Evan responsible for the ruined lifes of his friends, particularly that of Kayleigh, my friend who was his first love and to still wants.
Determined to carry out what he don't could do during his childhood, Evan travels back in time and tries to rewrite history for that his loved ones don't suffer the traumatic experiences they had. By changing the past Evan hopes to transform the present. However, every time Evan changes something in the past, discovers his return to the present that his actions have unexpected and disastrous consequences. However much he tries, is unable to create a reality that allow that he and Kayleigh live happily.