Francis, an intelligent and cynical cat, is moved to a gloomy, dilapidated house with his owner Gustav Löbel, a romance writer and archeologist. The top floor of the house gives off a mysterious and distinctly chemical odor. During Francis's exploratory tour of the house, he discovers the body of a cat who was killed by a bite to the neck. At the crime scene, he meets and befriends Bluebeard, a foul-mouthed, one-eyed and mutilated Maine Coon. Soon, Francis discovers another body and the fact that his house's top floor is the meeting site of a sect of cats led by Joker; the members of the sect worship an entity named Claudandus and perform ritualistic suicide by throwing themselves in an electric current. When Francis's cover is blown, he is chased by the sect members through the city's rooftops. He escapes through a skylight and meets a blind cat named Felicity, who supplies Francis with information on the Claudandus sect.