In a city park, two young girls’ bodies are found at intervals of several days. The cause of death is an artificially induced heart pathology. Police colonels Gurov and Kryachko suspect intentional murder. But who could commit such an intricate crime? The detectives examine the victims’ surroundings and reach a medical center operating underground—researching rare heart diseases. Gurov begins to understand its activities and comes to a terrible conclusion: the murdered girls are not the last victims of a bloody series…