Anna and her boyfriend Florian celebrate passing their high school graduation exams with a trip in a rubber dinghy. A speeding motorboat brings their happiness to an abrupt end. Anna manages to save herself, but Florian dies as a result of the collision.

When a yacht ties up to his sailboat, it's nothing out of the ordinary for Nils. But a blow from the boom sweeps Nils off the deck and into Lake Constance. Paul Schott first spots the sailboat adrift and then the young man floating dead next to the boat.

Fire on board. At the deepest point of Lake Constance, millionaire heiress Marita Schiller is forced to flee her yacht wearing a life jacket. Along with her boat, an expensive piece of jewelry she had kept in an onboard safe also goes down with it.