Parasitic aliens arrive in the Southwestern US during the time of the Anasazi, seeking suitable hosts for their species. The aliens, known as the Users, find human hosts to be too large for optimal parasitization, forcing them to use immature forms and maintain large breeding ranches. This necessitates the consumption of most of a human child's brain to accommodate the alien host within the skull, a process that requires discarding hosts every few years.

The premise of 'Anasazi' sets up a grim and visceral science fiction horror narrative, focusing on the parasitic nature of the alien Users and their brutal methods of host acquisition. The story appears to explore themes of survival, exploitation, and the horrific consequences of alien colonization on a primitive human population. The inclusion of additional short stories suggests a collection that offers varied explorations within the science fiction genre. The narrative framework likely emphasizes the aliens' perspective and their cold, calculated approach to their parasitic needs.