A school class returns from the tidal flats without their teacher. Did he die when the tide came in, or did a few students take advantage of the situation to get rid of their hated teacher? When a body is recovered, the case takes a new turn with the appearance of BKA officer Elisabeth Fädli (Natalie Belitski): The dead man from the mudflats is not the teacher, but a colleague from the BKA. Like Fädli and other colleagues, he had been assigned to monitor Gerd Eichinger (Harald Windisch), a sex offender with a high risk of recidivism who is currently in the city of Norden. Ann Kathrin is driven by the question of what really happened in the Watt and sets her sights on the BKA officers. Even though her boss Ubbo Heide (Kai Maertens) disagrees, Ann Kathrin is convinced that Elisabeth Fädli and her colleague Schröter (Jan Krauter) are the key to the case and know more than they are admitting. (ZDF)