College student Evan Treborn (Ashton Kutcher) is afflicted with headaches so painful that he frequently blacks out. While unconscious, Evan is able to travel back in time to difficult moments in his childhood. He can also alter the past for friends, like Kayleigh (Amy Smart), who was molested by her father (Eric Stoltz). But changing the past can drastically alter the present, and Evan finds himself in nightmarish alternate realities, including one where he's locked away in prison.