Investigating a colony whose settlers should be, but for some reason are not, threatened by radiation, Kirk and a landing party beam down to investigate. McCoy diagnoses the colonists as being in fine health and none of them wish to leave, no matter how much danger they are in. Spock, with Leila, an old acquaintance who has a crush on him, is infested by spores from a plant while examining the colony grounds. McCoy also soon falls victims to the spores, which leave their victims - even Spock - in a stupor with no desire to leave...and Kirk is left with a ship and no crew.
