The city is preparing to tear down a parking garage and build a children's park in its place. Only one thing is holding up the demolition: Adrian Monk, who has chained himself to a pillar in the basement. When the foreman confronts him, Adrian throws the key down a sewer grate. He refuses to let them tear down the parking garage where his wife Trudy died. Natalie arrives but doesn't have much luck convincing Adrian to give up his cause. Councilwoman Eileen Hill pays a visit and tries to convince Adrian to leave. He explains that the demolition could destroy possible evidence in Trudy's murder. Touched and impressed by Adrian's years of service, Hill agrees to have the city council take a second vote on the matter in four days time, since the vote was 4-3.
On the day of the council meeting, Adrian is at the pier helping Stottlemeyer investigate the deaths of two German tourists. Despite the fact he wants to go to the meeting, Adrian notices that one of the tourists has a broken camera strip on his wrist. Since nothing else is missing, Adrian deduces that the thief wanted the camera and that the couple witnessed a crime in progress. He then leaves for the council meeting. At City Hall, he and Natalie run into reporter Pawl Crawford, who wants to do a story on Adrian and says he's glad the parking garage isn't being torn down: he needs the parking. Outside the council chamber, they run into Adrian's nemesis, councilman Harold Krenshaw. Harold offers to vote against the demolition if Adrian will tell him who his new therapist is. Adrian refuses since they don't need Harold's vote now that Hill is switching her vote. However, as they prepare to go in, Disher arrives to tell them that Hill's sister has filed a missing person report.
The city council delays the vote and Adrian and Natalie visit Hill's office. They run afoul of Hill's pregnant secretary, Maria Schecter, who is clearly incompetent and doesn't like the irritated Adrian. They finally convince her to show them Hill's appointment schedule and they discover her last meeting was with Crawford. Stottlemeyer takes Adrian along as he talks to Crawford, who has no idea that Hill has disappeared or where she's gone. Hill's car has turned up empty and they wonder if she might have been depressed or drinking heavily. Crawford says that she wasn't as far as he was aware of, and that she wasn't drinking now. He tells them that Hill met with him to discuss his article on contaminated hot dogs, and she planned to shut down George Gionopolis, the hot dog czar, after she finished her meeting with Crawford.
The team goes to Gionopolis' plant, which is filthy. Gionopolis claims he hasn't seen Hill in weeks but she had set up an appointment with him on the day she disappeared. However, she never arrived. Adrian suggests that Hill did arrive and Gionopolis killed her. Gionopolis denies it and invites them to get a search warrant, saying he wouldn't be stupid enough to hide the body where they could find it.
Later, a desperate Adrian puts up "missing" posters for Hill. Natalie finds him and tells him that Gionopolis passed a polygraph test and surveillance footage confirms Hill wasn't at the plant on the day in question. Adrian visits Dr. Bell and asks him to put up a poster, and Bell suggests that Adrian is hanging onto the parking garage for reasons that have nothing to do with evidence. Adrian admits that he can't let them tear down the wall that was the last thing Trudy saw. Bell wonders if Adrian has recovered enough to let go of the past but Adrian refuses to accept that. The doctor suggests that Hill got bored with all the council meetings, and explains that he was on a city council and sent his secretary to cast his proxy vote. Adrian gets an idea.
Adrian goes back to Hill's office and tries to woo Maria so she'll cast a proxy vote for Hill against the demolition. They have lunch (Gionopolis' hot dogs) and Maria explains that she got the secretarial job when she saw that Hill had put up a help wanted ad at her Lamaze class. She got the job after a very brief interview and a drug test. Maria is reluctant to cast Hill's vote without ironclad evidence that Hill planned to vote against the demolition. She mentions that Hill had a journal and explains that the councilwoman kept it at her second apartment that no one else knew about.
Adrian and Natalie go to Hill's apartment and find that she was using it to meet with her lover. They can't find a clue indicating who Hill's lover was, but Natalie does find a positive pregnancy test.
Hill's corpse surfaces at the pier.
Stottlemeyer calls Adrian in to update him on the situation. Hill died at the same time as the German tourists and was strangled with a custom-made British necktie. However, Natalie and Adrian are surprised to learn that Hill wasn't pregnant. They do find Hill's journal in her purse and Adrian gets it to Mia.
At the council meeting, Harold calls for a brief prayer for Hill and then calls the vote. Maria is sitting in Hill's place and informs them that Adrian sent her Hill's journal, and highlighted the part where Hill said she'd vote against the demolition. She casts her vote against and the parking garage is saved.
The council calls a recess and Natalie and Adrian run into Maria, Harold, and Crawford in the hallway. A giddy Adrian offers to buy everyone drinks but then realizes that Maria can't drink. With that, he realizes what happened. The married Crawford was Hill's secret lover. When they talked to Crawford, he said that Hill "wasn't drinking now." Adrian points out that Hill couldn't have possibly hired the incompetent Maria because of her job skills. The councilwoman hired Maria for the sole purpose of getting a drug test for her, then using her urine to fake the pregnancy test for Crawford. She hoped Crawford would leave his wife, but instead he killed her then dumped the body at the pier. When he noticed the German tourists nearby taking photos, he wasn't sure if they captured the murder on film so he killed them too. Crawford points out that Adrian has no evidence. In response, the detective reaches forward and reveals that Crawford wears a custom-made British necktie, just like the one used to murder Hill.
Unfortunately, Maria has been listening and heard Adrian say how incompetent she is. Angry, she changes her vote and Harold gleefully takes it down. He then tricks Natalie into revealing Dr. Bell's name.
Later, Adrian looks regretfully at the wall where Trudy died. Natalie gently leads him out, past a sign saying the garage is being torn down to make way for the Trudy Monk Memorial Playground.
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