Gabriel Bach and Holly Valentin, investigators from the Hamburg State Criminal Police Office (LKA) and the Federal Criminal Police Office (BKA), are working to prevent a potential terrorist attack in the Hanseatic city. Raza, a German-Afghan substitute teacher who doesn't really have anything to do with crime, becomes vulnerable to blackmail after an incident with the police at a party. Gabriel and Holly then use him as an informant in the Islamist scene. Dadir, brother of the murdered drug dealer Youssef, seems to be the right initial contact for him. Raza soon provides another interesting lead. The terrorist El Adoua is said to have actually met with the ominous "Big Shot". Although Gabriel is now investigating the Islamist milieu, he seems unable to escape his past as an undercover investigator in neo-Nazi groups: As "Charlie," he mingles with his old "friends". Will this relapse jeopardize his current investigation and possibly even his private life?

Raza is being infiltrated as an informant by anti-terror investigators Gabriel and Holly, who are increasingly drawn into suspicious circles. There, it is suspected that drug dealer Gol Rahmani, alias "Big Shot," is planning a terrorist attack on the Hamburg Elbphilharmonie. Raza is becoming increasingly self-confident, allowing his old life to fade further into the background. Investigator Gabriel knows this temptation all too well: He finds it difficult to separate himself from his identity as an undercover investigator in neo-Nazi circles. As "Charlie", he visits his old "friends". His wife Emilia discovers that her husband never truly ended an affair in the right-wing extremist scene. Seeking help, she turns to Holly to learn more, but she remains silent about Gabriel's secrets. Both Gabriel and Raza must make decisions in their parallel lives that have serious consequences...