People are gathered to celebrate the demolition of a parking garage to make way for a playground. However, the workers have discovered one problem: Adrian Monk has chained himself to a pillar and throws the key down into the sewer. Monk explains to the foreman that he can't let them tear the parking garage down: his wife Trudy died there.
Natalie arrives and tries to determine what's going on. Councilwoman Eileen Hill arrives and is sympathetic toward Monk because of his years of service, but says hundred of children need the playground. Monk explains that Trudy's case is still open and they could be destroying vital evidence. Hill agrees to call for a second vote in four days since the first one was so close. Monk is left to inform Natalie she'll have to get the key out of the sewer.
Four days later, Stottlemeyer calls Monk to the scene of a murder at a pier where two German tourists were killed. Monk is busy checking his watch to make sure he doesn't meet the council meeting. However, he finds a torn camera strap on one victim's wrist but there's no sign of the camera and no signs of theft. Monk figures they were on the docks and saw something horrendous. However, he quickly leaves to get to the council meeting. They arrive and run into Paul Crawford, a reporter who wants to do a story on Monk. He insists he's on Monk's side and wishes them luck. With five minutes to go, they run into Harold Krenshaw, Monk's rival patient. He's a council member and notes he voted against Monk the last time. Harold suggests he might change his vote if Monk tells him who his new therapist is. Monk refuses, noting Hill is switching her vote so he doesn't need Harold's vote. Disher arrives to tell them that Hill's sister has reported the councilwoman missing.
The council postpones the vote and Monk and Natalie go to Hill's office. Her secretary, Maria Schecter, is trying to deal with all the phone calls and is distracted. She hasn't seen Hill in 24 hours, but knows the councilwoman had an appointment. Monk succeeds in irritating Maria, but they convince the pregnant Maria to print out the schedule and discover Hill's last appointment was with Crawford. Stottlemeyer and Disher go to see Crawford and take Monk and Natalie along. As they walk with Crawford, Monk tells the surprised Crawford that Hill has disappeared. They ask about the appointment and Crawford says that she had a few questions. They ask if she was depressed and Crawford notes that she wasn't, and that she isn't drinking now. They discussed his article about hot dog vendors and their lack of standards, and Hill planned to shut down George Gionopolis, a hot dog czar. She left Crawford to meet with Gionopolis.
The group go to Gionopolis' hot dog manufacturing plant where men spill hot dogs no the floor and cough on them. They meet with Gionopolis, who is glad to hear they're with Homicide rather than health inspectors. Gionopolis says he hasn't seen Hill in three weeks but she called him Monday morning, but never showed up. He admits that he hates her because she wants to regulate their business. Monk suggests Hill showed up and Gionopolis may have killed her. Gionopolis tells them to get a warrant if they want because if he had killer her, he would have disposed of the body where they'd never find it. Disher, who is eating one of the hot dogs, isn't sure what he's talking about.
Later, Monk is putting up posters for Hill and is so desperate he's offering a reward. Natalie arrives and tells him that they have surveillance footage showing Hill never went to Gionopolis' warehouse and he passed a polygraph test. Natalie insists that they'll find her eventually. Monk isn't so sure and goes to see Dr. Bell and get him to put up a poster. Bell refuses, and asks Monk if he really believes there's still evidence there. Monk admits that he doesn't believe it, but he knows the wall that was the last thing Trudy saw, and he can't live without it. Bell suggests that Monk has made enough progress that he can let it go. Monk refuses and Bell suggests Hill ran away, noting he used to be on a city council and got so tired of it he sent his secretary as his proxy.
Monk gets an idea and takes flowers to Hill's office. Hill's replacement is absent, so Monk tries to convince Maria to cast Hill's vote per the bylaws. He gives her the flowers and tries to flirt with her, and then ask her to lunch so he can tell her his side of the story. They go to get hot dogs and Monk reluctantly picks up the tab. Maria mentions that Hill posted a flyer at Maria'a Lamaze and she got the job after a brief interview and drug test. Monk brings up the parking garage and tries to convince her that the kids would be better off with a parking garage than a playground. Maria wonders if Hill planned to vote against tearing down the parking garage, and says that Hill kept a journal. When Monk notes they searched everywhere, Maria tells him that Hill had a second apartment.
Monk and Natalie go there while Monk complains about how stupid Maria is. They search the place and find fantasy costumes. Monk realizes the place was a love nest and they wonder who Hill was meeting with. Natalie finds a pregnancy test showing a positive result.
At the pier, Hill's body floats to the surface. Monk and Natalie go to the police station and the medical examiner confirms Hill died the same time as the tourists. She was strangled with a custom-made British necktie. The tests confirmed Hill wasn't pregnant, despite the test they found at her second apartment. Hill's purse was on the body and her journal is inside. Monk takes it and goes to City Hall. Harold is conducting the meeting and gives a short and somewhat distracted prayer in Eileen's honor. Maria is there and says Monk has given her a copy of Hill's journal with the important parts noted. Harold calls the vote on the parking garage and he and two other council members vote in favor of the demolition. Three others vote against it and Maria ponders for a long momentÃ¯Â¿Â½ then reads the journal and votes the way Hill planned to.
During the council meeting's recess, Monk runs into Crawford, Maria, and Harold. Even Harold is obliged to congratulate him. Monk's so happy he even offers to buy them drinks. They have to turn him down, but Monk realizes that Maria can't drink because she's pregnant. Monk realizes that Crawford was Hill's lover and killed her. He remembers that when they talked to Crawford before, he said that Hill wasn't drinking now. Here's what happened: Crawford thought Hill was pregnant and killed her to make sure his wife never found out. However, Hill wasn't pregnant. She hired Maria despite her incompetence (which Monk loudly proclaims) because Maria was pregnant, had her provide urine for a drug test, then used Maria's urine to fake the pregnancy test. She hoped to manipulate Crawford into leaving his wife. However, Crawford decided to kill her instead. However, the two tourists saw him as he dumped Hill's body so he killed them as well. Crawford points out there's no evidence, but Monk reaches forward and reveals that Crawford is wearing a custom made British necktie just like the one used to strangle Hill.
As Crawford is taken away, Maria turns against Monk for insulting her. Much to Harold's satisfaction, she changes her vote for revenge and walks away. Worse, Natalie lets slip the name of Monk's new therapist.
Monk goes to the parking garage and considers the wall that Trudy saw just before she died. Natalie comes to take him away. As they emerge, they pass a sign declaring the future site of the Trudy Monk Memorial Playground.