A murderous cult has emerged from the tunnels of Moscow’s underground, seeking vengeance through a series of grisly killings. But revenge for what? The police officer responsible for protecting the Second Subway is Agent Brezhov of the Federal Security Bureau. Assigned to track down trespassers at any cost, he leaves his two young sons at their mother’s deathbed. Now responsible for the care of his younger brother, Alexei is devastated by both his mother’s death and his father’s obsession with work. He clings to his mother’s Slavic pagan faith in Svetovid, the four-headed god who sees all. At school, Alexei befriends Kristina, an orphan who is being abused by her adoptive parents. Together, they begin to explore Moscow’s hidden tunnels. They find allies among the Diggers of the Underground, a group devoted to uncovering the secrets of the Second Subway. They also encounter a band of homeless street children who live in the abandoned metro station beneath the Bolshoi Theater. Bringing an unlikely sect together in the name of Svetovid, Alexei and Kristina set out to punish the families who have wronged them. They know they must risk everything to get justice for themselves and their siblings. Each of the conspirators will give their families one last chance to make amends. But is it too late? As Agent Brezhov struggles to make sense of the bloody crime scenes and catch the perpetrators, Alexei prays to Svetovid that his father would look just a little closer to home.