A woman, Ansara Waingaya, is shopping at a store and goes to the counter. The clerk rings up her items and they discuss that sheâ€™s from Nigeria and visiting for a week. She goes outside to a payphone and calls her husband Samuel, getting his answering machine. She says that she loves him and that she misses him and then hangs up. As she crosses the street, a van slams into her and drives away.
Monk is at home trying to read with Natalie reading over his shoulder. He finally gives her the magazine only to realize that someone is smoking bacon. He looks outside and sees an African man burning incense on a nearby street corner. Monk yells down to the man, who has no idea what heâ€™s talking about. Natalie gets a call and tells Monk they have a job. They go to the crime scene where Maria Fuentes, the housekeeper, was found dead. The owners, the Buxtons, just got back from Barbados and discovered their housekeeper, dead two weeks earlier and rotting ever since. Monk concludes she wasnâ€™t killed as the result of a crime of passion and notices that she has an earring in her pocket. He also sees a first aid manual on the corner. The bloodstains reveal that the killer opened the book to the page on head trauma before he killed the maid. Meanwhile, Randy tries to feign indifference to impress a female CSI technician, without a great deal of success.
That night, Monk canâ€™t sleep when he hears the same man from the street corner playing a pipe. Monk goes to confront the man, who explains he cannot leave the corner because his wife Ansara was killed there. The man, Samuel, shows Monk a picture of her to Monk and explains that she died there two weeks ago, and it is sacred ground. Monk brings Samuel back to his apartment, and Samuel explains Ansara was there for a two week teaching conference. He found shards from a headlamp in the road and explains he went to the police, but they havenâ€™t done anything yet. Monk asks him to make himself at home and Samuel starts smoking, much to Monkâ€™s dismay. However, he puts up with it and his him blow smoke into a garbage bag. Monk explains that heâ€™s a detective and heâ€™ll help Samuel find his wifeâ€™s killer. He shows the Nigerian newspaper clippings of his own dead wife, Trudy, and Samuel understands.
Monk and Natalie take Samuel to the police station and Stottlemeyer shows them footage they obtained from a gas station surveillance camera. It shows a van with a broken headlight driving by, but they havenâ€™t found it yet. Stottlemeyer warns such cases are difficult to solve but Samuel refuses to give up hope. However, once he leaves, Stottlemeyer tells Monk that itâ€™s foolish to try and build up Samuelâ€™s hopes, and he wants Monk to focus on Mariaâ€™s death. Monk refuses to help and explains about Samuelâ€™s wife. Monk goes back over the footage and discovers that the van driver turned around and headed back toward the hit-and-run corner.
Monk, Natalie, and Samuel go to the gas station and talk to two slackers. One of them remembers almost being hit by the driver and remembers the man was using his cell phone. The gas station is near a tunnel and Monk realizes the driver didnâ€™t want his phone call interrupted. The witness finally remembers it had big letters on it saying â€œPoison.â€
As Monk and Samuel do their laundry, Monk admits that most exterminator vans donâ€™t have â€œpoisonâ€ on them. Samuel realizes the van said â€œPoissonâ€: French for â€œfish.â€ He figures the van belongs to a French restaurant. Monk vows to bring justice for both of them.
Monk and Samuel go to Le Poisson Bleu and find a van. Samuel points out that the headlight has been repainted and thinks itâ€™s the same van. Monk isnâ€™t so sure but finds rice imbedded in the fender. Samuel remembers that Ansara was buying rice the night she died. The restaurant owner, Kenneth Nichols, fires an employee as they watch, and Samuel decides heâ€™s the killer.
Later, Monk is placing flowers at the street corner and Stottlemeyer arrives. The captain admits that Natalie talked to him and is worried about Monk, and tries to warn his friend not to fixate on Ansaraâ€™s murder. Monk plans to undercover at the restaurant with Samuel and get the evidence they need against Nichols, who has a record as a drunk driver. Stottlemeyer asks him not to and says heâ€™ll look into the matter. Monk agrees to think long and hard before doing anything stupid.
Shortly, Monk and Samuel work as dishwashers at the restaurant. It takes them a long time. They spot Nicholsâ€™ appointment calendar and notice that he was at a farmerâ€™s market on the night of the murder. Samuel thinks that Nichols was there, was drinking, and hit Ansara. Monk vows to help him get revenge if they confirm Nichols is the killer. However, he talks about how Ansara was married to him. Monk notices that John and Carolyn Buxton are visiting the restaurant. He realizes that Maria removed her earring because she was on the phone.
Disguising himself as a waiter, Monk goes to see the Buxtons. He confirms that theyâ€™ve known Nichols for years and offers his condolences about their housekeeper. They recognize him from the crime scene and Monk admits heâ€™s a detective. He talks to them and John explains that he left his cell phone in his house before he left for Barbados. Finally, Monk confirms that Nichols had Johnâ€™s cell phone number. Monk realizes that Nichols called Maria and calls Stottlemeyer to get a phone bill. However, Nichols takes them captive at gunpoint and orders them outside.
As Nichols drives them away from the restaurant in the van, filled with stinking fish, Samuel manages to get Monk to focus on the murder. He finally explains that Nichols was driving that night and called Buxton on his cell phone. Maria picked up the call and they talked for a minute, and Nichols hit Ansara. Nichols kept driving and Maria overheard everything. He kept her on the phone by claiming he was trying to help Ansara, and Maria opened the first aid book. Nichols went to the house and bludgeoned her to death.
Nichols drives out into the countryside and Monk is ready to die rather than smell more fish. Samuel tells him that their wives are with them now and that they have to be strong. Monk admits that heâ€™s confused Trudy with Ansara and is ready to give up. Samuel has Monk reach into his pants pocket, get his cigarette lighter, and ignite it to burn through the ropes. When Nichols opens the back gate, the two men drop the crates on him and Samuel hits him repeatedly. Finally he pulls out a photo of Ansara and demands that Nichols say her name. Monk then demands that he says Trudyâ€™s name.
Later, Samuel prepares to return to Nigeria and assures Monk that theyâ€™ll meet again and heâ€™ll come to visit him in Nigeria. Monk isnâ€™t so sure. The detective wonders what it feels like to know who has killed his wife, and Samuel says knowing is everything. He assures Monk that heâ€™ll know himself some day, and gives him his flute before going.