Doctor Who The Krotons

The TARDIS arrives on the unnamed planet of the Gonds who are ruled and taught in a form of selfperpetuating slavery by the alien Krotons crystalline beings whose ship the Dynatrope crashlanded 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