The main character of the book is a twelve-year-old boy, Seryozha. His journalist father brings into the house a man who appears to him to be a victim and with whose help he plans to conduct his journalistic investigation. But this is a maniac-murderer, and great efforts have been devoted to searching for him. The boy and the killer pass through the novel hand in hand - victim and persecutor. Their fight is rich in unexpected turns, since both have extraordinary thinking. The boy often wins with his unpredictability of actions. However, in the end he finds himself in a trap...The investigation is headed by Major Kandaurov.