The owner is arrested, the food bowl is empty – and all because of that pompous success guru Franz Frummelmann, whom – absurd thought! – the owner is supposed to have killed. Poisoned, with methanol. Cat Coco is not entirely convinced that the two investigating detectives are up to the task and decides: "I will investigate myself." To assist her, she enlists her feline housemates Maxi, Purzel, Merlin, Percy, and Goldie. Because while she is beautiful, smart, and self-confident (which she rightly believes), she is only a year old, still inexperienced in the twists and turns of criminal investigation, and somewhat distracted by her love for tomcat Felix from across the street. She soon discovers that a life as a private detective can be quite dangerous, especially when she starts researching at Frummelmann GmbH, the company of the murdered man.