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?

Nastya Olkhovskaya's department gets a new case. The owner and his mistress were killed in a country house. The killer was clearly not interested in the man — he killed him on the doorstep, and spent several hours with the woman, even cooked for her, and then drowned him in the bathroom, throwing rose petals into the water. It soon becomes clear that this is just the beginning — the killer of couples is not going to stop. And now danger threatens all couples in love in the city! Anton Shcherbatov, a consultant and data analyst, is involved in the case.