 An Enterprise landing party finds a planet biologically paradise-like, but soon a crew member is killed by something lurking around. An unidentified, irresistible force from the planet keeps the ship caught and blocks the transporters function. Suddenly a sort of spore eruption knocks Spock out, but only temporarily. They find a primitive village near the power source, devoted to the service of a certain Vall they seem to consider their divine creator; McCoy finds them completely free of disease, aging and natural dangers. They observe them sacrificing food to a temple, apparently housing the machine, which blocks out all other life forms, and instructs the villagers to learn to knock the intruders on the head with lethal force. Their plan is to attack it when in need of another feed...