Photographer and adventurer Frederick Plowright could not resist the offer of Professor Clark Ashton Scarsdale to join the "Great Northern Expedition". Its task is to explore the mysterious system of caves in the Black Mountains, which, according to the professor, holds the key to the future and the very survival of mankind. But in the caves of researchers meets and ancient horror... The novel by the English writer B. Copper is rightfully considered one of the best works inspired by the grandiose “Hitles of Madness” F. Lovecraft . The book continues in the Polaris series a number of publications related to the genre of "lost worlds" - an old and eternally new genre of fiction and adventure literature.