The radical animal rights organization TBF uncovers a doping scandal and suspects veterinarian Nina Berger of being partly responsible. The veterinarian is the mother of Piet's classmate Hanna and runs a practice where their dog Bagel is also vaccinated. When a stone flies through the practice window during treatment and a threatening letter from TBF appears, Piet begins to investigate. He discovers that Nina's daughter, Jule, is a staunch animal rights activist and that the two are at odds. But is she responsible for the attacks? Together, Piet and Hanna find new leads.