Earth, the distant future. Beaming down from the Nerva Beacon, the Doctor and his friends discover Earth is habitable once more. Unfortunately a Sontaran officer is conducting tests on a group of human colonists to determine their ability to withstand a full-scale invasion...
Elenco: William Hartnell , Patrick Troughton , Jon Pertwee , Tom Baker , Peter Davison , Colin Baker , Sylvester McCoy .