A man sneaks into boxing gym and cuts open a punching bag, then inserts a plastic explosive charge inside of it. The next morning, boxer Ray Regis and his coach Louie Flynn come in, discussing the championship they're competing for on the 25th of the month. They lost the championship five years ago and are just now getting a shot at it again. A washed-up and drunken old boxer, Eddie, has been sleeping the gym and staggers out to greet them. As he leaves he throws a punch at the bag to show how Ray should do it. The explosives goes off, killing him.
Stottlemeyer is working on a stolen art case when Monk and Natalie come in. The captain informs Monk that he has to pass a physical test required of all civilian crime scene consultants. Monk goes to the track with Natalie to practice but is in horrible shape. He's trying to get rid of a cramp when Stottlemeyer calls to the gym. While he and Disher wait for Monk, Stottlemeyer talks to the CSI tech who has determined that a motion-sensitive detonator was used for the bomb, and it was intended for Ray. They find a DNA sample on a thread and take it to the lab, and Monk staggers in. Ray has heard of Monk's reputation and is glad to have him there, but Monk says it will be his last case since he can't pass the physical.
An agonized Monk meet with Dr. Bell and says he plans on giving up. Dr. Bell doesn't believe it and warns that quitting can be additive, but Monk insists he'll be going on welfare along with Natalie if she needs to. He then goes back to the gym where Stottlemeyer and Disher are talking to Louie. When the captain asks about Louie's "World's Greatest Dad" mug, the trainer admits that he didn't do a very good job and his daughter died five years ago. The police have identified the DNA as belonging to The Iceman, a professional hitman. He doesn't come cheap so someone must hate Ray a lot. Louise says there's no one who hates Ray that much, including the Marino crime family who often use the Iceman. Louie refuses to let Ray back out of the championship match even though Stottlemeyer can't assure the boxer's safety. Monk is busy filling out his welfare application and an angry Stottlemeyer is upset that Monk would consider giving up, and wonders what Trudy would think. As Stottlemeyer leaves, Monk notices a photograph of Louie and Ray from the championship match on the wall.
Monk goes to visit Ray at a studio where he's voice-dubbing a commercial for deodorant, filmed at the expensive study of rich man Daniel MacGraw's house. After Ray finishes dubbing, the sound engineer runs some footage of the man busting in on the shoot, angry because his wife gave them permission to use the house without his knowledge. Monk asks for a moment alone with Ray despite the fact they need to finish the commercial by the beginning of the next month, and once alone reveals that he knows they threw the match: Louie wears a cross but hides it when he's lying, and he had it under his shirt in the photo. Monk has confirmed that Louie paid for his daughter's expensive treatment five years ago and had no other way to raise the money. Ray admits that he threw the fight for Louie so he could pay for his daughter's medical bills. Monk figures that the Marino family figured out what he did and now they want revenge. Ray wonders what Monk plans to do with the information but the detective concedes that Ray has suffered enough so he won't say anything.
The next morning, Ray comes to Monk's apartment at the crack of dawn and insists on paying Monk back by training him to get through the physical tests. The boxer begins a grueling regiment of exercise which has Monk exhausted and feeling hopeless about his chances. Meanwhile, Stottlemeyer and Disher go to see Frankie Marino, head of the family. Frankie says that he got the word that Ray wasn't going to win and bet heavily on him losing, so he made a bundle. Frankie says that he has word from the streets that someone wants Ray disposed of by the end of the month. Stottlemeyer believes him but wonders why the Iceman's employer isn't concerned that Ray die before the fight.
On the day of the fight, the Iceman gets into the arena as a food delivery man. The police have the place secured and Stottlemeyer brings Monk up to speed on Frankie's info. The police want to assign someone to be in Ray's corner but the boxer wants only one person: Monk. Meanwhile, the Iceman has gone up to one of the first-class booths with the food, tied up the spectators there, and has assembled a sniper's rifle to take out Ray.
The fight begins and Monk occupies himself making sure that Ray's socks and shoes are neat. When Ray starts sweating, Monk asks Natalie for deodorant and they notice the sniper rifle. Monk tells Natalie to keep the fight going so the Iceman doesn't get a clear shot, then runs up several ramps, jumps to an escalator, runs up the down escalator, and climbs over several balconies to get next to the Iceman's booth. Ray wins the fight and as he poses for the win, Monk jumps on the Iceman and distracts him long enough for Stottlemeyer and Disher to arrive. They're forced to shoot and kill the Iceman. As the police clean up the crime scene, Monk looks at the deodorant and realizes who hired the Iceman. He explains that MacGraw was buying the missing art that Stottlemeyer was investigating. He had it mounted in his study and was furious when his wife let the crew use it for Ray's commercial. he hired the Iceman to kill Ray, which would cause the company to pull the commercial so no one would see the pictures hanging on the wall in the ad. The police arrest MacGraw and take him away.
Later, Monk and Natalie visit the gym to let Louie and Ray know that Monk passed his physical. A now-overconfident Monk throws a few punches at Ray, who accidentally hits him and all but knocks him out.