The monstrously mutilated corpse of one of the employees was discovered in the Paris National Museum. Pinned to the body is a note with a strange inscription: “Degenerate Man.” And this is just one of the links in the chain of monstrous crimes taking place in the museum. The killer plays a sophisticated game, each time leaving clues for the investigators - plant leaves and excerpts from scientific works, minerals and open books... The police cannot find a connection between these symbolic signs. And then amateur detectives begin their own investigation: the famous anthropologist Peter Osmond, his colleague - the priest and scientist Father Magnani and the archive employee Leopoldina Devare...