The main character of the story is Professor Trojan, the head of a Prague clinic, who is not experiencing the happiest of times. His cat has been poisoned with cyanide, he has a falling out with his son Petr, who has moved to Brno to be with his wife, the promising singer Eva, and only seeks out his father when he needs money, and as if that weren't enough, someone shoots him in the evening. Trojan initially considers it a mistake or a prank and does not share the fears of those around him. But then cyanide is discovered and one of the patients takes it from the assistant Dvoracek, who borrowed it for an unauthorized experiment. Trojan pairs the cyanide with a gunshot and slowly begins to suspect that someone is trying to kill him. At first he suspects Dvorak, who might become the foreman after his death, but later, as he falls deeper and deeper into a psychosis of fear and apprehension, he begins to suspect everyone around him...