When the TARDIS arrives on the planet of the Gonds, the Doctor, Jamie and Zoe discover a world ruled and enslaved by the Krotons. The brightest Gonds are always chosen to serve as companions of the Krotons and are never seen again...

Zoe is selected as a companion for the Krotons and the Doctor insists on joining her.

Jamie is held prisoner by the Krotons who intend to recapture the Doctor and Zoe for their mental energy.

Selris succeeds in drawing the Krotons out of the Dynatrope but Eelek agrees to hand the Doctor and Zoe over to them in return for their leaving the planet.