When Captain Stottlemeyer's son Jared skips school to attend a rock music festival, Monk and Natalie join the captain at the festival to help look for him. Monk hates the atmosphere and wants to leave, but soon a roadie named Stork turns up dead of an apparent drug overdose. One of Stork's friends, a fellow roadie named Kendra, insists that Stork was killed. Kendra asks Monk to investigate, and he agrees.
Stork was found with a needle in his arm, but according to Kendra, Stork had quit taking drugs and was afraid of needles. Yet an acupuncturist at the festival confirms that she treated Stork that morning, and that he was looking to score some heroin. Either Stork was back on drugs and over his fear of needles, or something strange is going on. When Monk examines Stork's body, he finds clues that confirm Kendra's suspicions. Stork was indeed killed, but who killed him?
A guitar string found at the scene of Stork's death leads Monk to a rock star named Kris Kedder. Kedder denies any involvement in Stork's death, and Monk can't prove he was involved. But when Monk hears the lyrics to Kedder's newest hit song, a tune called "Peggy's Gone to Memphis," Monk solves the case.
Here's what happened. "Peggy's Gone to Memphis" wasn't written by Kris Kedder. Stork wrote it about his daughter, Margaret (Peggy is short for Margaret), and Kris Kedder stole it. When Stork confronted Kedder over the theft, Kedder killed Stork, and made it look like a drug overdose. When Kedder remembered that Stork was off drugs and afraid of needles, he disguised himself as Stork and went to the acupuncturist to make it seem like Stork had overcome his fear and relapsed into drug use.
According to Kendra, Stork always mailed a copy of his songs to himself as proof of his authorship. Unfortunately, Kris Kedder gets his hands on that copy before Monk can, and he quickly destroys the incriminating sheet music. There appears to be no evidence against Kedder, until Monk remembers something. The acupuncturist mentioned that Kedder, while he was pretending to be Stork, blew up a beach ball for a young girl. Since Kris Kedder uses a unique asthma inhaler, the air inside the beach ball could be traced back to Kedder and connect him to the murder.
Monk and the gang urgently scramble to find the incriminating beach ball, but after chasing the elusive ball all over the festival grounds, it winds up in the hands of Jared Stottlemeyer. Kris Kedder, Jared's hero, asks for the ball, but Jared decides to do the right thing and give the ball to his father. With the case solved and Stottlemeyer reunited with his son, Monk can finally leave the horrors of the rock festival behind him.