The year is 1967. A series of mysterious murders of women are taking place in Leningrad. Experienced KGB major Chubin and police captain Fedorov are assigned to catch a maniac who leaves mysterious signs next to the victims. 

Crimes occur at night in the area of the Obvodny Canal, in the very center of the city. The killer leaves unusual symbols painted in charcoal next to the victims. Major Chubin, who is investigating the case, has already encountered occult murders — a few years ago he tried to uncover a religious sect, but the mission failed, and he himself almost died. Now Chubin lives with a fear of the dark and a sense of guilt for an accidental murder. His partner becomes Captain Fedorov, a former policeman who is in love with his best friend's wife. Being under tremendous pressure from the leadership, they are trying to figure out the maniac and prevent future murders.