With Sharona out of town visiting her ailing mother, Monk has been left in the care of his annoying former neighbor, Kevin Dorfman. As Monk is forced to deal with Kevin's antics, there's a knock on the door. To his astonishment, it's Dwight Ellison, the father of his late wife, Trudy. Ellison is an executive overseeing a popular game show called "Treasure Chest." He's convinced the current champion is cheating, so he asks Monk to come to Los Angeles to help him figure out what's going on. Monk and Dwight head to L.A., with Kevin in tow.
When they arrive in LA, Ellison immediately takes Monk to the studio where the game show is taped. Monk meets Val Birch, the current champion, before another episode is taped. During the taping, Monk becomes convinced that Birch is working in tandem with Roddy Lankman, the show's host. But he's not sure how.
Later that night Monk goes to Ellison's house for dinner. All of his memories of Trudy come flooding back; this is her childhood home, after all. Monk cannot bring himself to enter Trudy's old bedroom - it's just too emotional for him. Talk turns back to the mystery at hand, and Ellison explains that Roddy Lankman's history is filled with turmoil - gambling debts, bankruptcy, and the recent unfortunate death of his personal assistant.
When Monk and Kevin check out the scene of the car crash that killed Lankman's personal assistant, they find evidence that Val Birch was at the scene! The mystery deepens, and Monk realizes that he has to get closer to the game show to break this case. Monk does the unthinkable: he asks Ellison to put him on the game show... as a contestant!
Once he's on the show, Monk's OCD comes to the surface as he fights the urge to clean a smudge off of his buzzer. But as the show progresses, he studies the interaction between Roddy Lankman and Val Birch closely... and solves the case! It turns out that Lankman has been manipulating the cards the questions are printed on, feeding the answers to Birch. But that's not all these two are guilty of: Val Birch had stumbled upon Roddy Lankman's assistant right after her "accident." With her last breath, she told Birch that Roddy had killed her. Birch, not a man to miss out on an opportunity for a payday, recorded her dying words and used the recording to blackmail Lankman. So when Lankman couldn't pay Birch's price, he decided to put him on the show as a contestant. The cheating was a way for Lankman to pay Birch off for the blackmail.
Back at the Ellison's house, Monk finally enters Trudy's room. Though he's filled with great sadness, he moves about her room, looking at her belongings. He can't bring her back, but ends up leaving with some solace... and renewed strength to find her killer.