Plot: The TARDIS arrives on the unnamed planet of the Gonds, who are ruled and taught in a form of self-perpetuating slavery by the alien Krotons — crystalline beings whose ship, the Dynatrope, crash-landed there thousands of years earlier after being damaged in a space battle. The Krotons are in suspended animation, in a crystalline slurry form, awaiting a time when they can be reconstituted by absorption of mental energy. Periodically, the two most brilliant Gond students are received into the Dynatrope, nominally to become "companions of the Krotons", but in truth to have their mental energy drained, after which they are killed.
Cyborg SheDoctor Who: Revenge of the CybermenDoctor Who: The DaleksThe StrongholdDoctor Who: Resurrection of the DaleksDoctor Who: The Robots of DeathDoctor Who: Horror of Fang RockThe Branom BoatSlaughterhouse-FiveA Knight in CamelotTime After TimeThe Time Traveler's WifeA.R.O.GBigglesHot Tub Time MachineDoctor Who: DragonfireDoctor Who: Delta and the BannermenDoctor Who: Time and the RaniDoctor Who: The MutantsDoctor Who: The Time Monster