A roadie, Stork, is looking for Kris Kedder the night before their concert. Stork finds Kedder and accuses him of stealing his song. Kedder claims ignorance but Stork isn't buying it so Kedder offers him $5,000. Stork refuses and warns him he's mailed a copy of the song sheets to himself for copyright protection. Kedder knocks Stork over the head, then takes a hit on his asthma inhaler as he considers the matter.
Natalie and Monk arrive at Stottlemeyer's office and Natalie wants to collect on a dry cleaning bill, over Monk's reluctance. Stottlemeyer gives them the runaround, since Disher is out sick, and then gets a call from his ex-wife about his son Jared. Jared has skipped school to go to a rock concert and Stottlemeyer goes to help him. Monk offers to go with him since he went to a lot of rock concerts as a boy.
They get to the rock concert and Monk realizes that he thought they were talking about a geology exhibit. He backs out and goes back to the car to wait for them. Stottlemeyer tries to show the security man a picture but it's badly out of date and he clearly hasn't seen Jared in a while. Monk tries to get the audience off of the car without much luck and tries to get a cab. He ends up mistaking a portajohn for a phone booth and staggers out to meet Natalie. They're interrupted when Stork's corpse falls out of an adjacent portajohn.
Kendra, Stork's girlfriend, finds them and says that Stork was phobic about needles even though he apparently died of a drug overdose. They check a map Stork had and Monk points out the victim was seeing an acupuncturist at the concert.
Meanwhile Stottlemeyer spots Disher at the concert and gets him to help find Jared. Monk, Natalie, and Kendra talk to the acupuncturist, who says Stork was looking to score some heroin and helped blow up a beach ball as he left. They check out the corpse and notice there is no mud on his boots, indicating someone carried him into the portajohn. Monk also notices that Stork couldn't have tied off the rubber strip himself and someone tied it for him.
Stottlemeyer and Disher find Jared and starts taking him out when Monk tells them about the murder. Stottlemeyer checks out the portajohn while Monk advises by radio from a safe distance (about 100'). Stottlemeyer finds a guitar string and Jared identifies it as a rare string that Kris Kedder used on his recent album. Monk figures out how the door was closed from the outside and they meet with the medical examiner while Stottlemeyer tries to bond with Jared. Jared notices his dad had an out-of-date photo and gives him grief over it.
Monk, Kendra, and Natalie talk to Kedder as he plays a song, "Peggy Goes to Memphis," and show him the guitar string. Monk clearly suspects Kedder and they go to Stork's trailer with Kedder trailing along. They notice Kedder uses a mint-scented asthma inhaler, and as they search the trailer Kedder steals an envelope. After he leaves, Monk notices it's gone and they find a receipt for a registered letter. Kendra remembers Stork mailing out a letter and Monk figures out Kedder was singing a song about Stork's daughter (Margaret, short for Peggy) so he stole Stork's song.
They go to confront Kedder who is up on stage performing. Kedder spots them and taunts them with the envelope containing the sheet music before tossing it into a flame pot. Monk puts it all together and tries to explain that Kedder went around and disguised himself as Stork and went to the acupuncturist and talked about finding heroin. Then he put Stork's body in the portajohn and locked it from the outside with a wire.
They have no evidence, but Monk realizes that Kedder (disguised as Stork) blew up a blue beach ball. The ball contains the air from Kedder's lungs, with the mint inhaler scent. If they can analyze the ball, they have enough evidence to arrest Kedder. Everyone chases after the beach ball without any luck. Monk goes up on stage and asks the crowd to cooperate. He doesn't have much luck and Kedder grabs a screwdriver and goes after the beach ball.
The ball lands up on a speaker platform and Jared grabs it. Kedder appeals to Jared but he hands the ball over to Stottlemeyer as Disher takes Kedder into custody. Stottlemeyer and Jared get their picture taken together with a little help from Disher.