A young man struggles to access sublimated childhood memories. He finds a technique that allows him to travel back into the past, to occupy his childhood body and change history. However, he soon finds that every change he makes has unexpected consequences.

Léon, the top hit man in New York, has earned a rep as an effective "cleaner". But when his next-door neighbors are wiped out by a loose-cannon DEA agent, he becomes the unwilling custodian of 12-year-old Mathilda. Before long, Mathilda's thoughts turn to revenge, and she considers following in Léon's footsteps.