The murder of a newborn baby and his mother is being investigated. To cover up his tracks and prove his innocence, the suspected doctor Pestov, who is also the father of the murdered child, donates someone else's blood for analysis. The examination establishes that the blood belongs to a pedophile, who is credited with a series of brutal rapes.

The Rescue Service receives an alarm call from a girl who begs to prevent the murder. Bobrova and Pankratov, who started the investigation, learn that the caller, Alena Erokhina, disappeared from the house without a trace. At the place of work they said that she was on maternity leave. Alena's former roommate Maxim Shcheglov and her sister Larisa fall under suspicion. But the young man did not know anything about the pregnancy of his girlfriend, and Larisa, despite constant quarrels with her sister, would hardly have decided on a crime.