Out they scampered from doors, windows, and gutters, rats of every size, all after the piper.
A rave meets near the river and everyone calls for Retchid Kat, the DJ. Backstage, Roddy Geiger, who performs as Retchid Kat, finally dons a giant cat mask and goes out to DJ the show. He begins and the crowd goes wild. Two of the girls in the audience text their friend, who is playing with a string quartet at the Von Hamelin Institute, a private school. Their teacher finally interrupts, telling that they'll have to stay all night if they have to and telling one of the players, Carter Brimley, to shape up.
After the rehearsal, the teacher, Paul Lawson, goes out to his car. As he gets in, he sees rats swarming over the seats. They attack him and rip him apart.
The next day, Assistant Principal Grace Kaplan arrives at school early and finds the dead man's car and his corpse inside. Nick is at home with Juliette when he gets called in, just as he discovers that they're refrigerator has broken down. He goes to the school with Hank and talk to Kaplan, who explains that she was the first one there and found Lawson's corpse. Sgt. Wu tells them that they've kept the car doors closed until Animal Control could arrive. When they finally open the doors, the rats swarm out and run away. The detectives find cages in the bushes, clearly marked Geiger Pest Control.
Nick and Hank go to see the quartet players, Carter, Trey, Marvin, and Sarah, who have a performance that Saturday. They don't know anything useful and saw no one in the parking lot. However, as they leave, one of the students tells them that Roddy Geiger goes to their school and that his father Ephram is an exterminator. The students explain that Roddy was suspended several days ago, and Sarah's mother says that the officers should talk to the school because it's not appropriate for them to talk to the kids.
The detectives go to see Geiger at his trailer. They hear violin music playing and investigate, and find Roddy playing music for the rats that he has in cages. Ephram interrupts them and demands to know why they're there. He insists that they had nothing to do with it, and figures that the police are trying to blame them for the death. When Roddy tries to run away, Hank grabs him and Ephram tells him to let go of his boy. Hank sees Mr. Geiger's face briefly transform into a ratlike visage and then the man attacks them. While Hank handcuffs Ephram, Roddy runs off and Hank goes after him. He finally tackles the boy, who says that he knows Nick is a Grimm and figures that he wants to kill him. Roddy's face also transforms and he attacks Nick, who easily knocks him down. Nick tells Roddy that he doesn't want to kill him, but warns that if he keeps it up then he's going to get hurt.
At the station, Hank interrogates Ephram and suggests that he cooperate. Ephram claims he was in the mountains the previous night, releasing the rats that he had captured. He can't provide an alibi for Roddy, and Hank points out that the boy was suspended for firing. Hank figures that set Ephram off and asks how the cages got to the school. The exterminator says that the cages were stolen and he didn't bother reporting them because the police wouldn't have been interested. Ephram insists that his son is a prodigy, but it didn't matter because the students never let Roddy forget that his father was an exterminator. When Ephram insists that his son didn't need Lawson because of his talent, Hank suggests that Roddy snapped.
Nick interrogates Roddy, who refuses to say why he was in a fight at school. When Roddy claims he knows everything he needs to about Grimms, Nick says that the students would say the same thing about Roddy. He points out that Roddy was suspended for fighting Carter and the others, and Roddy insists that they jumped him first. Roddy finally admits that he was at a rave the previous night but refuses to give the name of the host, Sammy, at first. When Nick warns him that he'll arrest Roddy otherwise, the boy gives them Sammy's name. They confirm that Roddy is Retchid Kat, the most famous raver in Portland. Sammy swears that Roddy was with him, and Nick figures that someone set Ephram up by leaving the cages there. They let Roddy go but hold onto Ephram.
Nick releases Roddy but admits that they still have to verify his father's alibi. Roddy figures that won't happen and storms off. Harper calls the partners down to the morgue and tells them that Lawson died of a heart attack. The teacher was on medication and the detectives wonder if it was a prank gone wrong or an attempt to scare Lawson to death. However, Harper says that there was no guarantee the scare would have killed him. She also autopsied a dead rat and examined its stomach. It ate fibers from something else in the car. The fibers are red and green, the same colors as the music school, and the partners go to check out Lawson's car and see if there's something in the car that matches the fibers. However, Captain Renard calls Nick and Hank in for an update on the case. He warns them that with an expensive private school involved, things could get sticky if politics get involved.
Roddy goes to see Sarah and tells her that his father has been arrested for Lawson's death. He wonders why she didn't say anything about how her friends beat him up, and Sarah says that Roddy is only someone she used to care about. He realizes that she's with Carter and kisses her. Sarah says that she can't keep sneaking out to be with him, and asks who put the rats in the car. Roddy figures that Carter did it to frame him and keep them apart. Mrs. Jessup comes out and orders her daughter into the house, and tells Roddy to stay away from her family. As Roddy goes, Carter drives up and asks why Roddy is there. When Roddy threatens to attack him, Carter warns him that he has 911 ready to speed dial. Roddy vows that he'll pay and leaves.
Renard meets with the press and assures them that they're making every effort to bring Lawson's killer to justice. Meanwhile, the partners get the lab report back on the fibers. Some came from an expensive car while others came from a blanket. Mrs. Jessup comes to the station to warn Nick and Hank that Roddy came to her house and is out of control. When Nick wonders why Roddy came to the Jessup house, Mrs. Jessup explains that he dated Sarah, and is worried that her husband will go out of control if he sees Roddy.
Once Nick takes Mrs. Jessup's statement, he goes to see Eddie. Eddie confirms that the Geigers are reinigen, non-violent scavengers who only fight back when pushed to their limit. Nick asks Eddie to talk to one of them and explains that Roddy is a violin prodigy. Eddie points out that his kind and reinigen aren't on good social terms. When Nick says that Roddy is an outsider, just like Eddie and Nick himself were, Eddie reluctantly agrees to help.
When Nick returns home, he finds that Juliette has called in a repairman for the refrigerator. The man cuts his hand and Juliette goes to get a bandage. When the repairman turns around, Nick realizes that he's a reinigen. The man realizes that Nick is a Grimm and runs off in a panic. Juliette wonders what happened and points out that a man running off when he sees Nick is kind of strange.
Hank and Woo go out drinking. After Hank ends up paying, he runs into Adalind Schade. They chat briefly and then Adalind offers to buy Hank in return for saving her life. He accepts and they go to the table, while Renard watches from the street.
Roddy is at his trailer practicing the violin. Eddie comes to see him and listens in awe to the music. When he applauds, Roddy comes out and asks who he is. When Eddie says that he's a friend of Nick's, Roddy tries to close the door but Eddie extends his claws and holds the door open. He goes in and explains that Nick isn't like the other Grimms that they've heard of. Eddie tells Roddy that he has true talent but doesn't recognize it. He tells the teenager not to throw it away, figures they're done, and says that sometimes lives collide in the most bizarre ways. Roddy doesn't know what to say and Eddie gives him his card as he leaves. Once Eddie leaves, Roddy gets a call from the station informing him that his father was injured resisting arrest and is in the infirmary for 48 hours.
As they come back with carryout, Juliette wonders why the repairman was scared of Nick. Eddie calls to tell Nick that he got through to Roddy.
After hearing about his father, Roddy tears up his room in frustration.
Later, Hank and Nick inform Renard that the fibers came from a SUV, and Carter is one of the few students who drives a BMW SUV. Renard tells them to get a warrant.
Roddy visits the rats in their cages and frees them. He then takes his Retchid Kat mask and his violin and walks away, unaware that he inadvertently started a fire.
At the Institute, Marvin warns Carter that Sarah had a visit from Roddy and knows that they did it. Sarah wonders if they did it, and Marvin figures that everyone knows that Carter got the chair because they framed Roddy for the fight. They get a text message with the location of the rave for that night.
Nick and Hank go to Carter's home to search his SUV. They check it out and find a blanket with holes, rat droppings, and fiber that matches the color taken from the rat's stomach. Mr. Brimley demands to see a lawyer until Hank threatens to put out a warrant for Carter. Mr. Brimley then tells them that Carter went out with his friends. A report comes in about the fire at the Geiger house. They arrive and realize that someone released the rats, and figure that whoever is responsible will go after Sarah.
Roddy goes to the docks with thousands of rats following him.
Nick and Hank go to the Jessup house and tell Mrs. Jessup that her daughter is in danger. She calls Sarah but realizes that her daughter left the phone there. Nick checks the call log and finds the rave address.
Sarah is in the car with Trey, Marvin, and Carter, going to the rave... unaware that Roddy sent them the address.
At the warehouse, Roddy lights hundreds of candles, plays the violin, and sends the rats out. Sarah and the others arrive and realize that they're the only ones there. They can hear the music playing and start to go inside, but Sarah asks them if they got Roddy suspended. Carter claims that they defended themselves and asks if she wants to be with Roddy. Rather than be left out, Sarah goes in with them. They hear the music playing in the basement and go downstairs, but Sarah hesitates before finally going along with the others.
Nick and Hank pull up outside and spot Trey's car, and then go inside.
Sarah and the others finally find the main basement chamber, lit up with the candles. Roddy is there, wearing his Retchid Kat mask, and accuses them of killing Lawson. Sarah realizes that the others lied to them. Roddy starts playing and they realize that he's Retchid Kat. The rats start attacking the teenagers, and the boys run off while Sarah trips. The rats swarm her just as Nick and Hank arrive. Hank fires off shots, scaring off the rats, and Nick pulls the remaining rats off of the girl while Roddy walks away.
Later, the boys confess to the prank gone wrong and Sarah asks Hank and Woo to tell Roddy that she's sorry. Meanwhile, Nick follows Roddy and finds the teenager waiting for him. The detective tells Roddy that Sarah knew nothing about the prank, and asks the boy if it was worth it. Roddy insists that they deserved it and that they wouldn't have confessed if he hadn't acted. Nick points out that nobody got hurt, but Roddy reminds him that Lawson wasn't so lucky.
Nick brings pizza to Hank at the station. Hank wonders what they'll charge Roddy with, and Nick figures that there is nothing they can charge him with. He points out that no one would believe a report on music and rats and violins. Hank wonders how Roddy got all the rats there but ends up dismissing it as a fluke. When he opens the pizza box, he discovers that Nick has left him a rubber rat, and promises that he'll get revenge.
The next day, the repairman comes back to the house. Juliette is there and the repairman says that he came back to get his tools. The man insists that he never did anything bad and Nick has no reason to come after him, and then scurries off.