A home nurse, Cassie Drake, is on the phone talking to the niece of her patient, an elderly man named Joseph Moody, that she's taking care of. The niece is coming over in 40 minutes to see her uncle. After Drake hangs up, she tells Joseph that he needs to remember what happened in 1968 at the Hampton Street Depository. Joseph rambles on and she tells him he had his chance… and wheels him up the stairs. She then shoves him down the stairs where he falls to his death.
A woman is listening to her daughter practice the piano when two policemen come over to inform her they've had another noise complaint. They figure it's the same guy who made the pervious complaints. They leave and Monk and Natalie watch from next door. The girl starts practicing again and Monk is clearly at the end of his rope. Natalie can't even hear the piano but Monk admits that he tried to call Dr. Kroger, who recently passed away from a heart attack. Natalie promises they'll find another therapist but Monk admits he was really messed up before he met Kroger. Monk isn't satisfied with any of the other therapists he's met and starts screaming at the girl again.
At the police station, Monk is trying to find a mystery to solve while Stottlemeyer has Randy help him study for the maritime exam. It turns out both of them know Morse code. Monk discovers the case about Joseph, which was closed when the police declared it an accident. Monk insists on checking it out and they go to the house. Monk notices the house is for sale and starts focusing on the fixtures while Joseph's niece explains that she was coming to visit. Stottlemeyer notes that Drake said Joseph was taking a new medication and Miss Moody admits her uncle could walk short distances. Drake said that Joseph walked up the stairs then fell. Miss Moody breaks down crying, and Monk tries to get more information about the house from her. Stottlemeyer draws him off to the side to tell him he shouldn't be making big decisions right now, and should go home and get some sleep. Monk goes ahead and buys the house.
Monk and Natalie go to the office of Dr. Neven Bell, a brilliant therapist and teacher. Dr. Bell comes out and shakes hands, and even has wipes and the right brand of bottled water on hand. Bell has Dr. Kroger's painting, and admits he misses Kroger as well. Bell gets to work and tries to find out why Monk isn't sleeping, and notes the piano playing has only been bothering Monk since Kroger died. The girl is playing Chopin and Kroger liked Chopin, and Bell figures that it's reminding Monk of Kroger. He suggests Monk is buying the house to deal with Kroger's death. Monk doesn't feel comfortable and gets up to leave, but then realizes he can't leave early or Natalie will kill him. They just sit quietly.
Later, Monk goes to a hardware store for fixtures and explains to the hardware store clerk about his problems. The clerk leaves and another worker, Jake Phillips, offers to help and gives Monk his card. Later, the workers are moving Monk's items in and Monk tries to help. He shows Natalie around the house and she wonders how he's coping with the fact he's no longer living where Trudy lived. She warns that Monk is responsible for any problems with the house but accepts his decision. She proposes a toast… and Monk notices the light fixture isn't centered. She quickly leaves as Monk starts obsessing about the furniture.
Monk calls Jake over to move the fixture and he notices that the light isn't up to code. He finds more problems and calls over a plumber, Ramon. They start taking apart the house to get at the corroded pipes. Monk and Natalie are cowering on the stairs, and Monk notices scuff marks on the wood. Following the marks upward, he sees a rip in the wallpaper. He checks on Moody's wheelchair and notices it matches the marks on the stairs. He concludes that Drake lied about Joseph walking up the stairs, and she lied about it.
Drake returns home to find someone waiting for her: Jake. He tells her that Monk is on them and kills her with an awl.
Monk and Natalie get Stottlemeyer and Disher to go to Cassie's to follow up on Monk's suspicions. They find her dead but Monk notices that although someone tried to make it look like an interrupted burglary, nothing was taken or searched. Disher finds $4,000 in 1960s currency and Stottlemeyer runs a trace. Monk goes home and starts cleaning up. Jake gives Monk some good news: Ramone is getting married. He then warns that he's found some mold and Monk has no choice but to let him go to work removing it. They find a box in the attic with a collection of boring news articles.
Stottlemeyer talks to the depository worker, who reveals that the money was part of a stolen shipment back in 1968. Two of the robbers died in prison but they never gave up the name of the third robber.
Monk and Natalie go through Moody's clippings, and Monk notices that all of the articles have stories about the depository robbery on the other side. Monk notices Jake's tool belt and sees an awl: the murder weapon. Jake pulls a gun on him and Natalie. He chains them to the bathtub. Monk explains that Moody stole the money, suffered from dementia, and started blabbing to Drake about the money. She killed him before he could talk to anyone else, and now Jake is looking for the hidden money. Natalie manages to get a hammer and they try to crawl away, pulling the bathtub with them. Monk pounds a nail straight: just because it was driving him crazy. Monk notices something in the wall and Jake notices and breaks in the wall. It turns out the light wasn't centered because there was a false wall. They take down the wall and find the money, and Jake shoots his partner Ramone. He keeps tearing down the wall for the money, while Monk and Natalie push the wall section down on him. They try to get to the door, still pulling the tub, and Natalie decides to call for help. She gets to the fireplace and sends up smoke signals in Morse code. At the depository, Stottlemeyer discovers that Moody was the inside man at the depository. They notice the smoke and realize Natalie is sending a SOS. Jake wakes up and prepares to shoot them, but Stottlemeyer and Disher show up just in time to take him into custody.
Monk decides to go see Bell and talk about his father, and things go well. Monk makes another appointment, two hours later that same day.
Back in his apartment, Monk is reading when he hears the neighbor girl play her Chopin piece. Having come to terms with Dr. Kroger's death, he smiles and opens the window so he can hear it clearer.