Edinburg, 1645. The city is in the throes of the worst plague in its history. No one knows who will be the next to succumb, no one save the Night Doctor, a masked figure that stalks the streets, seeking out those who will not live to see another day. But death is not the end. The Doctor, Bill, and Nardole discover that the living are being haunted by the recently departed, ghosts who do not know they are dead. And there are other creatures lurking in the shadows, slithering, creeping creatures filled with an insatiable hunger. The Doctor and his friends must face the terrifying secret of the Street of Sorrows, that something which has lain dormant for two hundred million years is due to destroy the entire city.