The Enterprise is summoned to aid an imperiled colony on Beta Psi III, but with an unusual condition: no men are allowed in the landing party. The planet, founded by the brilliant geneticist Juanita Alvarez, is inhabited solely by women, who want nothing to do with the male-dominated cultures that permeate the galaxy. But the survival of the colony is threatened by John Evans, a charismatic but ruthless drug lord who is after the native virula, which can be refined into the notorious drug nirvana, so powerful that one is addicted after a single dose. As Lt. Uhura and Dr. Chapel lead the landing party, they confront not only the threat to the colony but the challenges the colony itself poses to the patriarchal culture of the Federation. Chapel herself, now the bondmate of Commander Spock, struggles to reconcile her own conception of marital equality with the undeniably possessive nature of the Vulcan marriage bond.