Paul von Fock is uneasy when his friend Maria von Nottbeck confronts Justus von Brevern at a ball. The next morning, Justus is found dead at Paul's factory. As a court assessor, Paul must solve the crime while proving his innocence.
The suspects include Paul and Maria, who stole Brevern's notebook at the ball. Brevern's tent vanishes; Paul nearly drowns. His horses and gun are found at Sagadi. When attacked again, Paul suspects a plot to kill or frame him.
In Karula, Justus's room is found empty of his belongings. His mother is discovered dead, with counterfeit money as the only clue. The maid is found hanged. The notebook's mysterious entry is unlocked during an attack on Paul.
Paul survives the attack thanks to Maria's quick action. The mystery's solution leads them to Vihula, where the auction reveals the truth. Though Paul restores his reputation, one of the main characters is lost forever.
