People are mysteriously dying in the St. Petersburg metro, and witnesses of the accidents claim that shortly before they saw medieval knights in the tunnels... An underground river of water and sand, frozen under the city back in the seventies, has again begun to move, threatening to flood an entire metro line... How are these ominous events connected?

Journalist Oksana Lapteva, hoping to write a sensational article, accompanied by experienced diggers Kilovolt and Rouge, descends into the labyrinths of St. Petersburg dungeons. She still does not know that very soon they will have to defend their lives in a battle with the insidious and ruthless monster that lives in the darkness of the catacombs - the Metropolitan...