The first officially documented case of a Russian serial killer dates back to the beginning of the 20th century. A prostitute girl was found dead in St. Petersburg, killed in a particularly sophisticated way. Apparently, the murder was ritual, and the next victim is proof of this. Konstantin Marshal, assistant to the head of the capital's investigation, is looking for the criminal, but he masterfully confuses his tracks. Meanwhile, the killer is very close, and the life of the detective’s beloved woman hangs by a thread. The novel is based on real events.