Monk is cleaning his apartment when his vacuum cleaner gets jammed. In the process of fixing the vacuum, he gets a cloud of dust in his face. He panics and calls for Natalie. When the dust clears, Monk is shocked to find that someone has responded to his calls, but it's not Natalie. It's Sharona!
Natalie arrives. Monk reacts like a spouse caught cheating, but Natalie and Sharona are happy to meet each other. It turns out that Sharona's in town to sue a country club over the untimely death of her uncle Howie, who fell down some stairs on the club's golf course. The good relations between Natalie and Sharona end, however, when Natalie discovers that Monk paid Sharona more than he pays her.
The country club offers Sharona a huge settlement, but Monk examines the pictures from her uncle's "accidental" death and finds something amiss. Sharona, who barely knew her uncle, doesn't want Monk to discover anything that could jeopardize her monetary windfall, and begs Monk not to investigate, but it's no use. Sharona reluctantly joins Monk and Natalie as they go to the golf course to look around.
At the country club, Monk questions the two witnesses to Howie's fall - famous golfer Perry Walsh and his caddie, Gary. Walsh gives his account of what happened. Walsh was playing golf when he and Gary saw Uncle Howie fall down a set of stairs near the course's 14th hole. Gary tried to call for help, but his cell phone battery was dead, so he ran off to find aid. Walsh tended to Howie but could not save him.
After further examination of the scene and photos, Monk suspects that Howie wasn't playing golf the day he died, but was in fact trying to fall down the stairs intentionally in the hopes of suing the country club. But Monk is afraid to share his theory with Sharona.
At police HQ, Sharona reunites with Captain Stottlemeyer and Lt. Disher, both of whom are happy to see her, especially Disher, who can't get over how great she looks. Police records show that Uncle Howie had a history of suspicious "falls," but Sharona still holds out hope that her uncle's death was a true accident.
Monk continues the investigation at Uncle Howie's apartment and discovers some cushions on the kitchen floor, where Howie was obviously rehearsing for his "accidental" fall. It's clear that Uncle Howie was a con man, and that he fell on purpose so he could sue the club. Sharona is upset at the prospect of losing the settlement money, while Natalie argues that Sharona should be more concerned about the circumstances of her uncle's death. The two argue, and Monk is miserable.
Monk, Natalie and Sharona go to Perry Walsh's apartment to dig a little deeper. Natalie and Sharona bicker over whether Monk should take the stairs or the elevator. In the apartment, Monk notices a romance novel series on Walsh's bookshelf - they saw a volume from the same series earlier in Uncle Howie's place! When Walsh goes to get them refreshments, Monk tells Sharona and Natalie that Walsh is the guy. Walsh's wife must have left the book at Howie's place during a romantic rendezvous. Sharona pulls Monk and Natalie into a closet so Monk can give a full summation.
Monk explains that Walsh knew his wife was having an affair with Howie, and devised a diabolical way to get his revenge. Walsh went to Howie with a plan to con the country club. Howie would fall and sue the club, with Walsh and the caddie as his witnesses. Howie fell as planned, but when the caddie ran to get help, Walsh put his true plan – a plan to kill Howie -- into action. While Howie lay prone on the ground, Walsh approached and bashed his head on the steps. Monk has solved the case, but unfortunately, Walsh has been standing outside the closet, listening to the whole summation. Walsh kicks Monk out of his apartment.
Back at police HQ, Stottlemeyer is furious that they let Walsh know he's a suspect. Stottlemeyer blames Natalie, who blames Sharona, whom Disher defends, and soon they're all fighting so much that they don't notice Monk has disappeared.
Natalie and Sharona bond over their concern for Monk. Sharona admits she admires Natalie's patience in dealing with Monk, and Natalie thanks Sharona for being there when Monk was at his worst. The women search for Monk and find him at the cemetery visiting Trudy's grave, and the three agree-they have to take Walsh down.
They break into Walsh's office at the country club, where Monk finds a cell phone battery from the caddie's cell phone. Monk makes a realization. On the day Howie was killed, Walsh must have replaced the caddie's cell battery with a dead one, so the caddie would need to leave the scene to find help, thus providing Walsh enough time alone with Howie to kill him. If this is what happened, Walsh's fingerprints must be inside the caddie's cell phone, which would be impossible for Walsh to explain. Walsh overhears their conversation and rushes onto the golf course to find the caddie and destroy the evidence.
Natalie and Sharona hijack a golf cart while Monk chases after Walsh on foot. Walsh punches Monk in the face, but Natalie and Sharona don't give up, and together they take Walsh down and grab the caddie's cell phone for evidence. As they leave, Sharona trips on the stairs (which the club never repaired) and breaks her arm. There's going to be a settlement after all!
Natalie and Monk say an emotional goodbye to Sharona. They offer her a ride to the airport, but she says a friend is taking her. Disher pulls up, and to Natalie and Monk's complete shock they kiss, and then drive off together.