The USS Enterprise makes contact with the Theluvians, the native inhabitants of Syntagus Theluv. Their greetings are friendly, but the ship is suddenly fired upon from the planet. An away team transports down but is also attacked. The away team subdues their foes and all are picked up by a Theluvian ship, where they learn that the Theluvians age backwards - the "adults" who attacked them are actually children playing a game, and the "children" who picked them up are adults.