Clara Bardés, granddaughter of a famous deceased painter, has been hired to restore a series of paintings, some dating from the Middle Ages, which are preserved in the Notre-Dame Cathedral in Paris. During a solitary visit to the upper part of the building, when the tourists have already left, she notices the deformed silhouette of Ergaster, a perverse torturer whom she believed to be dead and of whom she could have been another victim, along with Professor Alba Longa, had it not been for the fact that, at the last moment, Commissioner Tynianov intervened. The cathedral closed behind her, and the criminal, who had apparently not seen her, remained inside. Once in her apartment, terrified, she called Alba Longa and he contacted Tynianov. Between the three of them, pulling the thread of the presence in the cathedral of this murderer, a specialist in the so-called "death of a thousand cuts," they discover a terrible conspiracy, the disastrous consequences of which are expected for the next few days.