Evan Treborn grows up in a small town with his single, working mother and his friends. He suffers from memory blackouts where he suddenly finds himself somewhere else, confused. Evan's friends and mother hardly believe him, thinking he makes it up just to get out of trouble. As Evan grows up he has fewer of these blackouts until he seems to have recovered. Since the age of seven he has written a diary of his blackout moments so he can remember what happens. One day at college he starts to read one of his old diaries, and suddenly a flashback hits him like a brick!

Nick Larson and his best friends Trevor Eastman and Amanda are celebrating the twentieth-fourth birthday of his girlfriend Julie Miller in a beautiful lake on a Sunday morning. Nick is expecting to be promoted in the company where he works, and Julie is planning to move to his place instead of going to New York for her Master degree. However, Nick is called by his colleague Dave Bristol, who is disputing the promotion with Nick, for a meeting with a client. While on the road, Nick has an accident and Julie and his friends die. One year later, Nick finds that he can travel in time and tries to fix the past, with tragic consequences for the future.

Sam Reide has the ability of traveling to the past and works with the police department solving unresolved crimes, witnessing the events with the support of his sister, Jenna Reide and reporting the criminal's identity to detective Dan Glenn. When Elizabeth Brown, the sister of his former girlfriend Rebecca Brown that was murdered a couple of years ago pays a visit to him, she tells him that she has just found Rebecca's journal with evidences that Lonnie Flennons, who was accused for the murder is innocent. Sam decides to witness the murder of Rebecca and his interference affects the future. He travels to the past to try to fix his mistakes, but every time he returns, the future is in worse condition.