Trieblings at the large Alpsee near Immenstadt is a tranquil little place, perfect for a relaxing summer vacation. At least that's what Christiane thinks, who is divorced and now a single by choice. She shares accommodations at the Riedlehof with geologist Karim from Füssen. On the very first evening, the family's cousin, Hannes Steidle, celebrates his bachelor party by the lakeshore. However, the pleasant party night abruptly ends with the flashing blue lights of the police and fire department. Because one person is missing.