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.

With an introduction to Monk's talent, his phobia's, and need for an assistant, Monk investigates the murder of the candidate bodyguard and a political worker. He determines the candidate was not the intended target.

When a woman drives off the road to her death, her body is mysteriously found the next morning by a psychic known for fudging the truth. Monk must discover if she's telling the truth this time, or else let a murderer go free.

After twenty-two-month-old Tommy Graser finds a severed finger and gives it to a policeman, Monk walks through the park with Tommy trying to retrace the child's steps. He finds no body or other incriminating evidence, but he does discover a surprising affection for the placid and intelligent toddler, who constantly repeats Monk's name and quietly submits to having his hands wiped when he touches ""nature."" A lab technician identifies the finger as that of a twenty-five-year-old man, and Monk deduces from a callus that the young man played the violin. After visiting the home of Daniel Carlyle, a musician who fits this description, Monk concludes that Daniel's mother and her other son, Jason, killed Daniel and that Jason is masquerading as his brother. Meanwhile, little Tommy is temporarily removed from the custody of his foster parents, and Monk surprises everyone, including himself, by volunteering to care for him for two weeks until his new adoptive parents can take him. With Tommy in

Monk appears to have met his match when a fellow detective shows up at a crime scene knowing all the answers.