Plot synopsis: The diabolically brilliant doctor Dr. Knock from Karlsruhe takes over a rural doctor's practice in Bavaria. To achieve his goal of a lucrative sanatorium, he must overcome empty waiting rooms, empty coffers and gullible citizens. And so Dr. Knock intrigues ruthlessly. He succeeds in acquiring power, prestige and the desired property. But what is the deal with the blue letters with no sender that flutter into the practice?