It's late, and Monk and Natalie are at a deserted highway rest area. They're there to meet a man who claims to have information about Trudy's murder. Monk has brought an envelope of reward money, and he makes Natalie hide so he can meet the man alone. When the man turns out to be a phony, Monk refuses to give him the cash. A struggle ensues. The man clunks Monk over the head, steals the reward money and Monk's wallet, and dumps Monk's unconscious body on a flatbed truck. When Natalie reappears, Monk and the man are both gone.
Monk wakes up on the back of the truck in a sleepy, forgotten town called Purnell, Wyoming. He's confused, his wallet is gone, and he can't remember who he is. The driver of the truck gives Monk five dollars and goes on his way. A woman named Cora notices Monk, looking lost, wander into a small café. Inside, Monk meets a kind waitress named Debbie who serves him a meal.
Meanwhile, back in San Francisco, Natalie, Capt. Stottlemeyer and Lt. Disher are frantically trying to locate Monk, as well as his assailant. In Wyoming, Monk is trying to understand who he is. He notices that he has these strange personality quirks. He's afraid of heights, he needs to keep his food separated, and he needs to wash his hands all the time. Monk is slowly being reintroduced to ... himself.
Monk goes to the local sheriff for help, and while he's there, Cora, the woman who spotted him earlier, shows up and claims that Monk is her husband. Unable to dispute her, Monk soon finds himself living in Cora's house, obediently doing every chore she asks him to do. She tells him his name is Jerry, and that he's a roofer.
Meanwhile, a few miles away, something strange happens. A local big shot named Roger Zisk plows his car into a bee farm. Zisk scurries out of his car and gets stung by hundreds of bees. Then, when Monk returns to the café to pay back some money he owed Debbie, he learns that she's gone. Apparently, she moved to Denver to be with a new boyfriend. But Monk's detective skills bubble to the surface. He notices clues that indicate that Debbie didn't leave town on her own volition. In fact, Monk thinks Debbie has been murdered.
Monk goes to talk to the sheriff, who's at the bee farm investigating Roger Zisk's accident. Monk tries to convince the sheriff that Debbie was murdered, but as he does, he starts to find things wrong with Zisk's story of his car accident. Did Zisk drive into that bee farm on purpose? Something fishy is going on, and Monk thinks there might be a connection between Zisk's car accident and Debbie's disappearance.
But Cora discourages Monk from his detective work. She's more interested in getting Monk into bed. When she mentions going to the town's bee-infested Lookout Point, Monk makes a realization. He's solved the case!
Monk goes to Lookout Point and meets the sheriff. He explains what happened: Roger Zisk and Debbie the waitress were having an affair. Debbie found out she was pregnant and threatened to tell Zisk's wife. Zisk killed her, and dumped her body at the bee-infested "Lookout Point." Zisk got stung by hundreds of bees. Eventually, Debbie's body would be found in the bee-infested area, and Zisk would have to explain his bee-stings. So he drove his car into the bee farm and intentionally got stung by hundreds of bees - again!
Just as Monk finishes his summation, Natalie arrives with Captain Stottlemeyer and Lt. Disher. Eventually, they tracked down the truck driver who dropped off Monk, and he pointed them in the right direction. When Monk sees his friends, everything starts to come back to him. Now Monk can return to being a great detective in San Francisco, where he belongs.