A rat in the house? Beissl gives Ava an ultimatum: either she locks her rat Nemo in a cage or she has to leave. But before he can finish the fight with his Berlin relative and her furry friend, Jerry delivers another piece of bad news: Quirin Gruber is found dead in his stonemasonry workshop, buried under a massive slab of stone. Dr. Hartmann discovers he was bludgeoned to death.

Biologist Valerie Lemke dies after a visit to a glacier. Dr. Hartmann quickly determines that she was pushed into the abyss. Jerry and Sophia investigate among her colleagues. Dr. Magda Hansen was a rival for Professor Gruber's affections, while Christian Wenzel was an environmental activist and a jilted lover. Even pharmaceutical manager Oliver Gross falls under suspicion because Lemke's research on blood algae was commercially lucrative.