A scandal involving fake stallion sperm, a mysterious horse grave, and a somewhat too attractive riding instructor – Stuttgart veterinarian and journalist Antonia has her hands full at the Marbach State Stud. When a stable hand dies under mysterious circumstances at the Lauterquelle, Antonia fears for her daughter Paula's safety as long as she works as an apprentice at the stallion station. The broad-shouldered Norbert also shows a striking interest in the fraud. Strangely, the fan of Black Forest cold-blooded horses always appears just when things get dangerous for Antonia.