 The Enterprise is called to an advanced planet to help with an emergency. Beaming down, though, they can find no people, only their cities. Suddenly, one of the away team seems to disappear from Dr. McCoy s sight. After the away team beams back up, a series of strange things begin to occur. One such thing is the appearance of an alien device installed to the life support machinery, which can t be removed because it s protected by a powerful force field. Going back up to the bridge, Capt Kirk notices everyone on the bridge is slowing down to a near-stop. He s been hyper-accelerated in time, so that he moves at super-speed compared to the crew. He then meets the aliens they beamed down to help: the Scalosians. They ve been stuck in hyper-acceleration since radiation poisoned their planet s water supply. Their men are also sterile, so they must lure space vessels to recruit males for reproductive purposes. Kirk finds his missing crewman, who seems to relish his new life; he s helped the Scalosians install the device to the life support, which will freeze the crew so that there will be a fresh supply of fertile males for generations. But a simple injury inflicted by a Scalosian man causes the crewman s body to age to death in mere minutes. Kirk rebels, but then pretends to accede to the Scalosians  plan. Meanwhile, the bridge crew saw Kirk vanish. Spock investigates, and figures out that they have hyper-accelerated invaders. He and McCoy isolate the acceleration factor and its cure. Spock accelerates himself, and finds Kirk. Together, they defeat the aliens and banish them back to their planet. Kirk then takes the cure, while Spock remains hyper-accelerated until he undoes all the modifications the Scalosians had made to the Enterprise.