The narrative begins as a desperate warning against a planned Antarctic expedition, presented by a geologist from Miskatonic University who led a previous scientific journey. Equipped with innovative drilling technology and airplanes, the expedition aims to collect deep-level rock specimens and upper fossils from the desolate continent. After establishing a base near Mount Erebus, the leader of the biology department, Lake, becomes obsessed with a strange, star-shaped marking found in ancient pre-Cambrian slate and pushes northwest into unexplored territory with a secondary party. Contact is lost after Lake discovers a series of towering, non-volcanic mountains higher than the Himalayas and unearths an underground cavern filled with perfectly preserved prehistoric specimens of an unknown, highly complex radiata species.
These entities, dubbed the Elder Things, possess a bizarre mix of animal and vegetable characteristics, leathery toughness, and a history preceding terrestrial life. When the narrator and the remaining team fly to the mountain camp to investigate the sudden silence, they discover a scene of unspeakable horror. The men and sled dogs have been brutally slaughtered, mangled, and dissected, and several monstrous specimens have been buried in strange star-mounded graves.
Alongside student Danforth, the narrator undertakes a harrowing flight across the massive mountain range to survey the hidden transmontane world. They find a colossal, geometrically eurythmic stone city of cyclopean architecture, abandoned for millions of years. Through extensive mural carvings on the decadent structures, they decipher the terrifying history of the Elder Things: their arrival from the stars, their creation of life and the subservient protoplasmic Shoggoths, their ancient wars with cosmic spawn, and their eventual retreat underground before the advancing ice age. Driven by morbid curiosity, the two explorers descend into a subglacial tunnel leading to the dark abyss of a sunless subterranean sea.
There, they encounter fresh evidence of slaughter, realizing that surviving Elder Things have been hunted and decapitated by mutated Shoggoths that have broken free of their control. Fleeing in blind terror from an onrushing, shapeless mass of bubbling protoplasm that mimics the mocking cries of its former masters, the explorers barely escape with their sanity. They return to civilization with a vow of strict silence, hoping to deter further exploration of a frozen realm where matter and time have forged a blasphemous alliance.
