The Enterpise is approached by an ion-propelled craft (much to Eng. Scott’s liking); from it enters a female who renders everyone unconscious. When the crew wakes up, McCoy finds Spock alive in sick bay but with his brain surgically removed. McCoy urges its quick restoration if he’s to survive at all. Desperately Kirk follows an ion-trail to a system where he gambles on an icy planet populated by a simple-minded all-male race of large cavemen who attack them. The landing party captures one, who says Kirk and crew are small like ‘The Others’ – bringers of pain and delight – whom they fear. McCoy brings down Spock’s body, mobilized with a mechanical brain-substitute installed. They enter the acclimatized, underground dwelling of ‘The Others’ – a similarly simple-minded all-female race of enslavers – and overpower female Luma by surprise. Kirk makes communicator contact with Spock, who knows not where he is but is aware of autonomic functions. As they finally find Kara, the female brain-thief, she overpowers them and, outfitting them with control belts, brings them before a female panel to be judged. As their interrogation commences, they realize there is no superior intellect among them capable of handling the technology to maintain the subterranean complex, and the ‘controller’ to which these women begin to refer is actually Spock’s brain, which Kirk must somehow get back and reunite with Spock’s body.