Cadet Jahna arrives on Nelding, a backwater planet, as a volunteer in an interstellar peace corps. The First Fathers of Nelding, a brooding, repressive group, requested her particularly - surprisingly, for she is young and unexperienced. Her first impressions are gloomy. Jahna is delivered to the huge fog fortress, Pengalen, where she learns, first, that she is to be assigned the care of infants and, secondly, from Becklord, the mysterious but attractive lord of Pengalen, that there is another culture on Nelding, a forest community called Tentback which is considered unclean and inhuman by the First Fathers and their followers.

Tentback is inhabited by people called mock-dirads, the mutated descendants of human colonists, born deformed and cast out by the First Fathers. They have mysteriously become protean, have imitated the native dirads and grown to look like them. Becklord sees the danger of becoming too alien to preserve civilization of any kind and pland that Jahna become a template, a pattern for imitation for female infaants (for the ability to imitate is lost in early childhood). Becklord is opposed by the First Fathers, by certain mock-dirads, and by Zuniin, an insane Tentback mother, tortured by hatred and fear, who will kill Jahna before letting her "steal" Tentback babies.

Conflict increases, culminating in violent warfare. Jahna must choose to stay in Tentback and become the Starmother or retreat to civilization.