A junior high school boy, Klaus Mollert, is at home playing video games. In the next room, his babysitter and her boyfriend are making out. Klaus drinks an energy drink and then picks up a real gun and shoots his TV screen. He then walks into the next room, kills the babysitter and the boyfriend, and then kills the parakeet when it tweets too loudly.
Gunter and Karl are called in the next day and Gunter tells his partner that he wanted the case because it restored his faith in young people. Mrs. Mollert insists that Klaus is a good boy and Gunter expresses his admiration for the killer. Karl draws him to the side and tells him to avoid contradicting Mrs. Mollert, and the hitman is glad to do so when she blames herself. The detectives check Klaus' room and find the walls covered with violent posters and video games. Gunter is still admiring the boy and Karl wonders what his parents were like and Gunter points out that they tried to drown him when he was a baby. However he assures Karl that he was simply born on the dark side. As they search the room, Karl finds an email from someone named Fassbinder with a picture of a gun, while Gunter notices that Klaus had dozens of energy drink cans.
Tannhauser has brought in a chess champion to play against him. The crime lord loses again and the champion apologizes, but Tannhauser assures that he wins wars while his opponent wins battle. Martine comes in with word that his new partner called to say the recent drug shipment arrived safely in Tangiers thanks to Tannhauser's new shipping method. Satisfied, the crime lord boasts that he's checkmated Racken. The champion congratulates Martine on her pregnancy and asks if it's a boy or a girl. Tannhauser starts to ask her as well but then says it doesn't matter as long as it's his.
The police lock Klaus up in an interrogation room and the boy has a psychotic episode. Braden confirms that he has designer drugs in his system and Gunter goes in to talk to Klaus. He takes a blow dryer and a colander of unpopped popcorn with him and offers the popcorn as a snack to Klaus. Gunter asks about Fassbinder and Klaus refuses to answer, so Gunter pours the popcorn down his throat and uses the blow dryer on it. Choking, Klaus finally tells him that he knows Fassbinder from school and that he gave him the drugs and the gun.
Gunter and Karl go to the school and talk to Klaus' teacher, who tells them that Klaus has had problems since his father left home. As they talk, one girl vomits and two boys fight, and Gunter points out that the teacher has no control over the She starts flirting with him and Gunter flirts back, while Karl gets her to explain that Fassbinder is the school custodian, not a student. The teacher takes them to Fassbinder, who starts running immediately and firing back with a gun. The detectives chase him into a courtyard basketball game and Gunter guns down three of the players while trying to hit Fassbinder. Karl accidentally kills the fourth player when he charges at them, and Fassbinder dies from a heart attack.
Back at the station, Braden tells Gunter and Karl that Fassbinder had designer drugs in his system as well. Gunter has already figured out that the drugs are in the energy drinks. Klaus and Fassbinder both had them and the school machine has the drinks as well. The partners go to the drink's manufacturing, Glücklichkeit Beverages, and talk to the owner, Rolf Dortmunder. He insists that no one at company would have tampered with the energy drink but refuses to let them search the place. Karl promises to come back the next day with a warrant and the detectives leave. Dortmunder's assistant, Mrs. Bartleby, comes in and he tells her that the truck driver must have screwed up the delivery and taken some of the spiked cans to the school. When she wonders what they should do with the remaining cans, Dortmunder gets an idea.
That night, Gunter visits Klaus at the hospital and tells the boy that the people who spiked the cans are responsible for Klaus' outburst and Fassbinder's heart attack. He assures Klaus that because he wasn't in control of his actions, he will only have to spend a few years in a mental hospital. Klaus doesn't believe him and Gunter assures him that adults lie all the time to children. The hitman admits that he has a son coming and he hopes that it will be just like Klaus. Yanking at his restraints, Klaus complains that they hurt and Gunter frees him and walks away.
Tannhauser receives word from Martine about the misdelivery of the drugs. The crime lord figures that Racken is responsible since he controls the trucking industry in town. Martine informs Tannhauser that Dortmunder is disposing of the drugs but Tannhauser wants to see her ultrasound. When she shows it to him, the crime lord congratulates her on a good job.
Gunter has another nightmare about the Martine dressed in black and jerks awake. The teacher, in bed with him, tries to reassure him and they end up having sex. However, Martine calls before they finish and tells Gunter that Tannhauser doesn't believe the baby is his. When the teacher tries to interrupt, Gunter tells her to stop and Martine figures he's talking to her and hang sup. When the phone rings, Gunter discovers that it's Karl, who wants him at the station right away.
At Glücklichkeit, Dortmunder's people bring in their families to help our the contaminated energy drink down the toilets. Bartleby congratulates Dortmunder on his success and he shows her the box of cigars that Tannhauser sent him as a thank you gift. Bartleby goes to get some matches for the cigars while Dortmunder discovers too late that the cigar box contains explosives.
At the station, the police try to deal with the riots caused by the explosion at the factory. Braden drinks a fresh cup of coffee and spits it out, and Gunter realizes that the designer drugs are in the water system. Karl notes Gunter's disappointment and accuses him of wanting people to choose evil rather than be drugged into it. Klaus calls to tell Gunter that he's going back to school to be bad, and then hangs up and holds his teacher at gunpoint.
Karl and Gunter go to the school and learn that Klaus is holding his teacher hostage. Gunter goes in alone and confronts Klaus in his oom. The boy wants to demonstrate that he's evil rather than drugged by killing the teacher for giving him bad grades, but Gunter warns him that under the third strike law, he'll go to prison for a long time. The hitman tells Klaus to walk away and admits that he was wrong about him and that he isn't evil. Gunter finishes by telling Klaus that no matter what, women aren't worth going to prison for. Klaus gives the gun to his teacher... who shoots Gunter in the face for his sexist comment. Karl brings Mrs. Mollert in and she runs to her son, while Gunter laughs and tells his partner that he's getting used to having his face shot.
Later, the chess champion beats Tannhauser again but says that he's improving. As Martine watches, the crime lord beats his opponent to death.