The country is recovering after a nuclear war. At one of the construction sites in the anomalous zone, the “Ring” facility, communications suddenly disappear. What is it—an influence of external forces, a human factor, or experiments by the ultra-complex self-learning machine “Setun” that directs the work? To find out the causes, a commission headed by Major Tor Igorevich Karibsky goes in. The major will have to make a difficult decision— the most important one of his life. What miracle has a human done for an unexpected opponent? Who and why needed to carry out monstrous experiments on people? And can a machine become a person?