the serial is set on the mineral-rich human colony world of uxarieus in 2472. in the serial, the alien time traveller the third doctor (jon pertwee) and his travelling companion jo grant (katy manning) are sent by the time lords to uxarieus, where they discover a mining corporation has been faking monster attacks on the colonists. later, the master (roger delgado), one of the doctor's people, arrives in search of an ancient doomsday weapon created by the natives of the planet.