The barren planet Exxilon, some time in the future. The TARDIS is forced down by a total power failure and the Doctor and Sarah meet a stranded Earth crew who came here to mine for priceless medical supplies. But what is causing the power failures? And why have the Daleks come here too?
Elenco: William Hartnell , Patrick Troughton , Jon Pertwee , Tom Baker , Peter Davison , Colin Baker , Sylvester McCoy .