On Friday, the 13th, a young woman was killed in a city park in broad daylight. Two days later, a man was killed in another park at exactly 1:13 p.m. The killer is well versed in anatomy, because he kills with one stab of a knife. At first glance, the victims are completely random. So the killer is elusive? Or is it still possible to figure out his scheme? Investigator Nastya Olkhovskaya enlists a consultant, data analyst Anton Shcherbatov, to investigate. To catch the criminal, Nastya and Anton have to figure out how he chooses his victims. And what does the number 13 mean to him?