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...