A group making a pilgrimage through the Himalayas, hiding from a snowstorm, ends up in a cave in which they find a body covered with inscriptions. Among other signs, there is a clear warning - “Satan exists!” All members of the group, except for the instructor named Ike, die in the cave. Scientists begin large-scale research, as a result of which people learn that we are not alone on Earth, that in the depths of the planet there live humanoid creatures - homo hadalis (man of the abyss), who are nicknamed hadls. The underground inhabitants resist the invasion, they deal with uninvited guests extremely cruelly, and the coordinated actions of the hadls on a planetary scale presuppose the presence of centralized leadership...