Monk learns that he must pass a statewide physical fitness test if he wishes to continue working as a consultant for the San Francisco Police Department. Monk and Natalie go to a running track for some training, where Monk proves to be woefully out of shape. Their workout is interrupted by a phone call. There's been an explosion at a local boxing gym, and Stottlemeyer needs Monk's help.

At the gym, Monk is introduced to a professional boxer named Ray Regis. Regis had arrived at the gym that morning to begin a day of training for his next fight, a big rematch with the current champion, Carlos Hiraldo. One of Regis' friends, a vagabond named Eddie, died when he hit Regis' punching bag, detonating a bomb. The bomb was clearly intended for Regis, but neither Regis nor his trainer, Louie Flynn, can think of anyone who'd want Regis dead. Monk, convinced that he will never be able to pass the physical fitness test, announces that this will be his last case.

A break in the case comes when DNA found at the crime scene is found to match a professional hit-man known as the Iceman. The Iceman is a former employee of the Marino crime family, but Regis and Flynn continue to deny any underworld connections. Regardless, Regis' life is in serious danger, and Stottlemeyer suggests cancelling the upcoming fight. Flynn angrily refuses, and the pressure is on to find the Iceman and the person who hired him.