After discovering one of his most trusted colleagues has been murdered, Gereon comes to suspect that the killer was someone on the inside. Meanwhile the ballistics report in a police officer's murder casts suspicion on him.
Tropes:
- Boys Like Creepy Critters: Early on, Moritz is seeing playing around with a jar full of roaches which he then dumps on a couple having sex.
- Death Notification: Bruno has come to inform Jaenicke's parents of his death. A neighbor points out that they need to use the light-based switch that was built by Jaenicke for his parents.
- Dramatic Irony: The lead detective berates Boehm for assuming fate has placed the perpetrators directly in front of them, while both murderers are directly in front of them.
- Flies Equals Evil: We hear the sound of flies right before Moritz finds the corpse of Jaenicke.
- I Need a Freaking Drink: Exploited by the worker from the train yard who offers Charlotte a drink when she is sobbing in the trolley. She agrees, following him off to a car where she gets kidnapped.
- I Was Never Here: Gereon and Bruno's wife agree that their encounter at the apartment never took place.
- Key Under the Doormat: Charlotte wanders the city, trying to find a place to sleep. She knocks on Rudi’s door. When he fails to answer, she finds a key hidden inside the layered doormat.
- Nice Job Breaking It, Hero: Gereon switched the bullet that killed Saint Josef with a bullet fired from Krajewski's confiscated weapon now in Bruno's possession. Turns out the same gun killed Jaenicke – the police thus believe that the murders of Saint Josef and Jaenicke are connected, and Boehm strongly suspects Gereon.
- The Oner: The scene of Gereon letting himself into Bruno's apartment, retrieving Jaenicke's journal from his desk and avoiding his senile wife is shot in one, 4:20 minutes long, sequence.
- Professionals Do It on Desks: After Greta lets Fritz into the house, they have sex on Benda's office desk.
- Three-Way Sex: Charlotte walks in on Rudi in the midst of a threesome.
- Unresolved Sexual Tension: Gereon finds Charlotte sobbing in his office. In a moment of vulnerability it seems like they are going to kiss each other, but they break off at the last moment.
