Night Killer tells the story of Melanie Back. A woman who lost her memory due to severe trauma and no longer remembered what happened to her. Ten years ago, Melanie was raped by a man who tortured her psychologically. She suffered that violence and would have died if her husband hadn't intervened to save her.
Melanie now lives alone with her daughter in another state. She moved to Virginia on the advice of her psychiatrist. Everything seems to be going well for Melanie and her daughter, when she starts receiving strange phone calls from a man who says she knows her, who says she loves her and wants to meet her.
At the same time, the police are investigating a series of murders of young women. It hunts down a serial killer who first conquers them and then rapes them, killing them. Melanie follows the facts of this serial killer on television and becomes convinced that she is the same person who calls her.
The police don't believe her right away, but then checks her without telling her. Melanie's phone keeps ringing scaring her, she answers the phone and decides to meet him, but he doesn't show up. Melanie thinks she's crazy, she no longer distinguishes reality from her nightmares.
Her stalker seems to know her perfectly, he knows everything about her, she always knows what she does and where she is. Melanie is sure of being followed, but she can never see it. Melanie is more and more scared, she is afraid that the man who torments her on the phone is the same evening the killer the police are looking for.
Melanie does not want to relive the horror of the past that does not remember in detail but that terrifies and makes her suffer. Pain is the only thing that reminds us of terror. Melanie, exhausted from the nightmares that become more and more recurrent, decides to take her own life, throwing herself into the icy waters of the ocean in the middle of winter, after having swallowed many barbiturates.
But a man saves her at the last moment. The film's finale will reveal a completely unexpected story full of twists and turns, on the great secret that Melanie had removed from her memory that will free her forever from that old nightmare by paying a very expensive price.