After Michelle Cullman lures Jack Leverett to her apartment for an illicit tryst, Jack becomes furious when he discovers a hidden video camera. Jack and Michelle struggle over the camera, the fight escalates, and Michelle winds up dead. Jack wipes away his fingerprints, grabs the camera, and flees the scene.
The next day, Monk and Natalie arrive at Michelle Cullman's apartment to investigate. In addition to Capt. Stottlemeyer and Lt. Disher, there's a new face on the scene: a big time Hollywood actor named David Ruskin. Ruskin is set to play Monk in an upcoming movie, and he wants to follow Monk around as research for his new role. Monk is excited, but Natalie is concerned that Ruskin could hinder the recent progress Monk has made with Doctor Kroger. Monk ignores Natalie's warnings, and shows off for Ruskin by making several flashy deductions and discoveries at the crime scene.
The next day, Monk arrives at a pawnshop, with Ruskin still shadowing him, to investigate a second murder. An intruder smashed through the wall of a neighboring restaurant, entered the pawnshop, and stole thirty-five dollars and a cheap wristwatch. The shop's owner surprised the intruder, and the intruder killed the pawnshop owner with the owner's own gun. Monk can't figure out why the intruder stole so little, or why he had to smash through the wall of the neighboring restaurant.
Monk and Natalie soon find the pawnshop owner's gun in a nearby alley. There's a spec of blue glitter on the gun. Monk also found blue glitter at the scene of Michelle Cullman's murder, so Monk concludes that Michelle Cullman and the pawnshop owner must have been killed by the same person. Then, at Natalie's house, Monk notices a note that Julie tore up to keep Natalie from reading it. Eureka! Monk has solved the case.
Everyone meets at the restaurant next to the pawnshop, where Monk has the police reassemble the pieces of the broken wall from the pawnshop break-in. The restaurant features sketches of patrons on its walls, and Monk has realized that the whole point of the break-in was to destroy an incriminating sketch. Sure enough, when the wall is put back together, everyone can see a sketch of Jack Leverett with his victim, Michelle Cullman. The sketch proves that Jack was with Michelle the night she was killed, and it also shows Jack wearing a shirt that matches a piece of fabric found at the original crime scene.
Meanwhile, David Ruskin has completely lost it. He's fallen way too deep into the role of "Adrian Monk." Ruskin is going around San Francisco, dressed as Monk, looking for Trudy's killer. When someone, mistaking Ruskin for Monk, gives Ruskin the name of Jack Leverett as "the killer," Ruskin assumes that Jack is Trudy's killer, and jets off to Jack's car dealership, eager for revenge.
When Stottlemeyer and Disher arrive outside Jack's car dealership to arrest him, they're surprised to find that David Ruskin, still dressed as Monk, is already there. Ruskin has taken Jack Leverett hostage! Monk arrives, and enters the car dealership. It's Monk vs. Monk! Ruskin has a gun, but before he can pull the trigger on Jack, Monk heroically wrestles the gun away. The police rush in, and Jack Leverett is arrested. In his final moment as Adrian Monk, David Ruskin points out a new clue in Trudy's murder case. After that, David Ruskin's days playing Adrian Monk are over. And with Ruskin out of the picture, it's clear that there's only one man for the role of Adrian Monk, and that's ... Adrian Monk.