A detective story set in a youth mountaineering club. One of the members, Ivan Kočička, nicknamed Kocour, single-handedly investigates the mystery of the body of an unknown man, which he discovered in a cave on top of a rock.

On 25 April 1605, the knight Milota was killed by the royal armourers while escaping from the castle of Temice. However, the robbed treasures were not found in his possession. Almost 400 years later, Jindra, Tomas and eighteen-year-old Alena spend their holidays at the castle with their grandfather, the castellan. The castle needs repairs, but there is no money for them. Tomas and Jindra decide to find Milot's treasure, which could help the castle. The visitors are guided by Alena and two temporary workers, Roman and Petr. Among the tourists, Professor Horák, who shows a suspicious interest in the castle's collections, attracts the boys' attention...

This dramatic story concerns the fateful night of March 14-15, 1939, when President Dr. Emil Hácha was forced to sign a document legalizing the establishment of the so-called Protectorate of Bohemia and Moravia. Screenwriter J. S. Kupka conceived this historical event as a human drama about a man who is faced with the decision of whether to comply with Nazi dictates or risk bloodshed.