After work, walking along the embankment, Roman Tartalotov meets the cultist Lana. Even though he has nothing to do with the sermons she reads him, he keeps encountering her again and again—realizing that he has fallen in love.
Roman’s worried relatives find out that the cultists who preach by day on the embankment turn into “night butterflies” at night—fallen angels of sorts. But instead of turning Roman away from Lana, this makes him even more determined to help her. The only way to do it is by infiltrating the cult from within…