Grace Morland's playful statement in the presence of guests that she would rather die than wear a fashionable hat turned into a tragedy: the next morning she was found dead, and she was wearing just such a hat on her head. Police Inspector Cockrill, leading the investigation, comes to the conclusion: this was a “joking” from one of the guests who, on the eve of the murder, was in the house of a local landowner. In a military hospital, a patient dies during a simple operation. Medical error? Inspector Cockrill, who is tasked with understanding the circumstances of the tragedy, does not think so. He is convinced that the victim was killed in cold blood and that one of the doctors and nurses committed the crime. But who could be bothered by the murdered man - a local postman who never had enemies?