Geologist Donald Melnick lived a remarkable life. He is respected in the scientific community, his wife is a brilliant anthropologist, and his children have a bright future. But memories of a half-forgotten incident in Mexico are increasingly disturbing Donald, because it seems to him that something terrible happened to him then, connected with the legendary tribe, the search for which almost cost his wife her career. Since then, Donald has been deathly afraid of the dark. Trying to find out the truth, he gradually realizes that both his wife and children are hiding some secret, and the life he has so carefully built is being destroyed right before his eyes. Donald does not yet know that in his search he will encounter genuine horror of truly cosmic proportions, and that long-ago incident in Mexico is only the first of a whole series of events that call into question the inviolability of the very reality around.