In nineteenth-century Victorian England, a young widow finds that she has inherited more than her late husband's property: The Furnavals serve as the ancestral keepers of supernatural portals scattered around the globe. When demonic entities begin crossing over from the Netherworld, Lady Diana realizes that a war is brewing, and she must be the one to confront it.

Accompanied by a young Chinese sailor named Yi-kin, her feline guardian Mina, and a mysterious scholar, Stephen, Diana will begin a journey to solve the mystery of her husband's death and prevent the apocalypse.