A stasis box recovered from a vanished empire becomes a prize that the Kzinti want.
Spock, Uhura and Sulu travel in a shuttle with a stasis box from an ancient empire, the Slavers, and are intercepted by the Kzinti, a feline warrior race. The box holds a powerful weapon, and the crew must keep it from the Kzinti, who want to use it to conquer.
The story is based on the work of Larry Niven, and it introduced the Kzinti to Trek, although the episode is the only one without Kirk on screen. It is a tense action story and an unusual adaptation, which has made it a talking point among fans.