The mysterious death of a chimpanzee at Zurich Zoo keeps investigators Isabelle Grandjean (Anna Pieri Zuercher) and Tessa Ott (Carol Schuler) busy in the early hours of the morning. Everything points to murder. But dead monkeys do not fall within the remit of the homicide squad, at least that's how prosecutor Anita Wegenast (Rachel Braunschweig) sees it. Tessa Ott therefore wants to investigate on her own in her spare time.