Three days after her disappearance, Daria Ballhofer’s lifeless body is found in Lake Constance - all signs point to murder. Daria's mother Marlene (Regula Grauwiller) and her sister Sina (Miriam Fussenegger) suspect Daria's husband Victor (Marc Benjamin) who shows more interest in setting a new record in free diving, than in grieving his dead wife. What was the real state of their marriage? Why was Daria suddenly possessed by the spirits of Lake Constance right before her death? 
To solve the case, Luisa Hoffmann (Alina Fritsch) and Micha Oberländer (Matthias Koeberlin) dive deep into the fascinating world of free diving, where absolute tranquility and acute danger to life lie close together.