A former San Francisco police detective suffering from an extreme case of obsessive-compulsive disorder is called in to investigate an apparent assassination attempt of a mayoral candidate in which one of his bodyguards is killed.

A very tidy woman who resembles Trudy turns Monk's head while he's investigating a triple homicide. The only problem is, she's the prime suspect.

In an attempt to stabilize his shaky marriage, Captain Stottlemeyer redecorates his office with the New Age artifacts that his ""hippie wife,"" Karen, has given him, but he can't bring himself to watch the documentary that she spent forty-five thousand dollars to film. When Karen thinks that her documentary subject--the world's oldest man--was murdered, the captain rejects the suggestion as absurd but calls in Monk to pacify her. Unfortunately for the captain, Monk agrees with Karen, and Stottlemeyer finds himself on Monk's front porch with two packed suitcases. Monk, glad for a chance to repay the captain for helping him through his three-and-a-half year ""slump,"" invites him to stay as long as he needs to. Predictably, they both end up with frazzled nerves and very little sleep. Depressed over his own ""slump"" and his inability to solve a five-year-old case involving the death of a seventeen-year-old boy, the captain becomes even more despondent when Monk finds a clue that he missed in

Monk encounters an old crush from junior high when she hires him to discover why her housekeeper was killed and her favorite painting vandalized.

Monk is called to a murder at the location where he first heard of his wife's murder, and while Monk figures out who the assassin is, he doesn't know that the one who ordered the hit is also responsible for the death of Trudy. Knowing that Monk will eventually put all the pieces together, he orders Monk's death, and when all hope seems lost, Monk discovers something which could finally end his 12-year nightmare.