Mr. Murder is a suspense thriller novel by Dean Koontz that follows the story of a successful author whose life is turned upside down when he becomes the target of a psychopathic killer who is his doppelgänger.

The novel explores themes of identity, the nature of evil, and the impact of fame. The protagonist, a writer, must confront his own fears and the dark side of his existence as he battles against a maniac who seeks to destroy him.

When bestselling author Marty Stillwater is pursued by a man who looks exactly like him, he discovers that this man is a dangerous killer who wants to take over his life. As Marty fights for his survival, he uncovers a web of deceit and horror that challenges his understanding of reality.