Adrian Monk solves a murder mystery that centers on diamonds hidden in a couch.
Adrian Monk is an obsessive compulsive detective who helps the San Francisco Police Department with homicide cases. Natalie Teeger, his assistant, accompanies him, facilitating interaction between Monk and the rest of the world.
They are called out by Captain Stottlemeyer to a murder scene. Stottlemeyer's new assistant Lieutenant Amy Devlin resents their presence. The victim is Garson Dach, deputy district attorney, found dead in his driveway due to head trauma. He lies in his pajamas and bathrobe next to his trashed Audi. Monk declares that the paper boy is the murderer. Dach had gone outside to get the newspaper, had seen his trashed car and was squatting next to it. As he got up, the heavy paper hit him in the face and he fell backward, hitting his head on the driveway.
They are still on the scene when they get called out to another case. A man with the fake name of Jack Griffin has been found dead in his hotel room in the seedy Excelsior Hotel, with an old photo clutched in his hand. His personal effects include an old pair of binoculars. Monk confirms the opinion of the Medical Examiner that Griffin died from natural causes, namely cancer. He also makes the deduction that he has spent time in Mexico working on yachts and fishing boats. After looking at the photo (of a nurse and a little girl with a bicycle in front of a house), Natalie decides to solve the case of Griffin's real identity.
Natalie and Monk go back to the Excelsior to get the key to Griffin's room. They arrive while the crime-scene cleaning crew is busy on the scene. Monk is impressed by their meticulous cleaning and the clearing of “bio hazardous” material such as the matrass. The leader of the team is Jerry Yermo, a fan of Monk's work.
They get called out to another homicide. Casey Grover, the manager of a thrift-store, has been murdered, his throat cut with a knife. There are no signs of a break-in and nothing was stolen. Monk decides to stay to help the clean-up crew. The others in Jerry's crew are Gene Tiflin, Corinne Witt and William Tong.
Natalie starts investigating the Griffin case, with the help of Monk's brother Ambrose and his assistant and girlfriend, Yuki Nakamura. When she picks up Monk again, he has organized her a date with Jerry for that night. They have a good time and agree to meet again on the Friday night. Meanwhile Yuki finds out the location where Griffin's photo was taken.
There is another murder, in the same neighborhood. Mark Costa, a real estate appraiser and womanizer, is found by his married lover – naked on his bed with a kitchen knife in his chest. The house has been ransacked, but no valuables were stolen. One red couch has been ripped apart. Monk deduces that it is a serial killer, the same person who killed Grover.
Then there is yet another murder. Cheryl Strauss is found draped over her coffee table. She has been tortured and asphyxiated. Monk notes that one piece is missing from her four-piece living room set – the couch in Costa's house, which he got from the thrift-store, where Cheryl had taken it.
The investigating team sets off again to Costa's house before the cleaners get around to the couch. Monk comes to the conclusion that the killer went from Cheryl to Grover to Costa to find the couch and then back to Cheryl when he couldn't find what he had hidden in the couch. The detectives learn that Cheryl's ex-boyfriend, Rico Ramirez, had left half a million dollars' worth of diamonds behind before he was jailed for four years. He is now out on parole. He becomes the suspect.
Natalie investigates a lead on the identity of the nurse in Griffin's photo and finds out that her name is Stacey O'Quinn and her daughter was called Rose. Her husband Walter was presumed killed after he went sailing and never came back. After Walter's disappearance, Stacey found out that his business was deeply in debt. Natalie also finds the house on the photo and hears that one of the longtime residents saw Walter there a week ago. Jack Griffin was really Walter O'Quinn.
The next day there is another murder in the neighborhood. Stuart Hewson has been shot four times. His house is spotlessly clean, but his truck is dirty, which leads Monk to conclude that the scene was cleaned by the murderer. From other clues, they learn that Hewson had a telescope on a tripod focused on Costa's house. According to Monk, Hewson's murderers are Jerry Yermo and his team. They overheard the detectives' talk about the diamonds and when cleaning Costa's house, tore up the floorboards looking for them. Hewson saw them and demanded a cut of the spoils, after which they murdered him. All four cleaners are badly in debt.
The investigators now have a good theory, but no evidence. Natalie's date with Jerry is shipwrecked by Monk, whose attempt at undercover surveillance fails.
Amy Devlin goes undercover and makes a hit on William Tong at a fancy bar. She drugs his drink and with the help of Natalie takes him to Griffin's room at the Excelsior hotel, for which they still have the key. When he has passed out, they tie him near-naked to the bed. They then fake his murder with his car and his clothes and wallet and use this as a scare tactic on Corinne, telling her that Ramirez has come looking for his diamonds. She confesses.
Devlin then goes undercover as Corinne, trying to sell her diamonds, in order to flush out Ramirez. That night Ramirez slips into her motel room and tries to kill her, but is apprehended.
Natalie solves the case of Walter O'Quinn – he used the binoculars to watch the building opposite the Excelsior, where his daughter Rose (a.k.a. Alyssa) works as a waitress in the coffee bar. Natalie and Monk confront her with the truth, but she wants nothing to do with her dead father.
Best part of story, including ending:
Adrian Monk's obsessive compulsion makes for some interesting detective work.
Best scene in story:
When Monk visits his brother Ambrose and is met at the door by Ambrose and Yuki, both in bathrobes, fresh out of the shower, and it takes Monk a long time to realize that they are lovers.
Opinion about the main character:
I dislike Monk's obsession with disinfection and cleaning, but like his self-confidence in his own abilities.