When the Orion slaver Disr'ta'bilt ha Uldur discovers that two captives kidnapped by his deputy are Starfleet officers on shore leave, he quickly abandons them on an uncharted planet. Lt. Commander Christine Chapel, M.D. finds herself suddenly stranded with no food, no supplies, and no companionship other than an aloof Commander Spock, the half-human, half-Vulcan First Officer of the Enterprise. An ice-age winter is closing in, and Chapel quickly faces a medical emergency for which her sophisticated training is nearly useless.
They are found by the Domii, a small tribe of hunter-gatherers led by Domi, whose word is final except in matters of healing, where he must answer to the Adar Doma, the tribal healer. Taken on as an apprentice by the Adar Doma, and christened "Kista" in their language, Chapel discovers the richness of their folk medicine, and its heartbreaking limitations. But it is in her relationship with Spock that she experiences exasperation, rage, sufferingÑand ultimately joy.