Great Jumping Gobstoppers!
The Doctor, Zoe and Jamie have arrived on a planet ruled by the mysterious Krotons. The Doctor soon discovers there's a form of self-perpetuating slavery going on as the best and brightest of the local population, the Gonds, are being selected to become companions of the Krotons -- a fate from which they never return. Determined to put an end to this practice Zoe and the Doctor take a test which will allow them to become companions, but will they be accepted?