Frederick Plowright, a well-known scientific photographer, is recruited by Professor Clark Ashton Scarsdale to accompany his research team in search of “The Great White Space,” described in ancient and arcane texts as a portal leading to the extremities of the universe. Plowright, Scarsdale, and the rest of their crew embark on the Great Northern Expedition, traversing a terrifying and desolate landscape to the Black Mountains, where a passageway hundreds of feet high leads to a lost city miles below the surface of the earth. But the unsettling discoveries they make there are only a precursor of the true horror to follow. For the doorway of the Great White Space opens both ways, and something unspeakably evil has crossed over—a horrifying abomination that does not intend to let any of them return to the surface alive . . .