Kirk, Uhura and Chekov find themselves suddenly transported light years across the galaxy to the planet Triskelion. There, they are trained as thralls, slaves who engage in gladiatorial combat for the pleasure of the Providers, three faceless beings who amuse themselves by wagering on the outcomes. Outfitted with collars that inflict pain for disobedience, the thralls are submissive and pliant. Kirk eventually challenges the Providers to a wager that will either result in freedom for all or a lifetime of slavery.