At the Ronov castle, the archive-keeper professor Nykl (Milos Nedbal) is searching for the lost painting The Naked Shepherdess by the famous Fragonard. Nykl is just about to disassemble the mantelpiece in the knight's hall, convinced that the painting must be hidden somewhere inside. His efforts, however, meet the strong disapproval of the castle manager, Anna Juzová (Jirina Petrovická), who knows very well where The Naked Shepherdess is. She wants to get hold of the painting herself, to emigrate and smuggle it along. In fact, Anna deals with forgeries of the most distinguished old masters, selling them abroad. The copies are made for her by the painter and restorer Maudr (Martin Ruzek) and the certificates of authenticity are issued by Anna's companion - expert Laburda (Karel Höger). One day, Anna is found murdered in front of the castle's fireplace.
Based on the novel by Karel Capek, the prominent Czech writer of the early 20th century who coined the word robot for his play R.U.R., the story revolves around a discovery of Krakatit - a powerful explosive - by Prokop, an experimental scientist who, following an accidental explosion in his lab, slips in and out of delirium. When he realises that, in a delirious period, he has given the formula for making Krakatit to one of his colleagues, he tries to find the man, who does not realize how dangerous a thing Krakatit is. In the process, he nearly gives his discovery away again to foreign interests, a group of anarchists, and even greater forces of darkness...
After an attack against the guard of the Third Reich, Nazi repression intensifies, and the Czechoslovakian resistance's organized sabotage in an aircraft factory leads to Gestapo shootings.
