Someone harpooned Horst Flens, the caretaker of the Lübeck aquarium, and left him seriously injured. In addition, the attacker has kidnapped Otto, a very valuable puffer fish that is the pet and star of the aquarium, and has left an extortion note. Later, while the victim is in the hospital in a coma, Finn Kiesewetter and his team begin the investigation by questioning the caregiver's colleagues.
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