three time lords meet at an observatory and discuss the theft of confidential files relating to "the doomsday weapon." they begrudgingly realise that only one man can help them so the third doctor, accidentally accompanied by jo grant, is temporarily released from his exile and sent in the tardis to the desert planet of uxarieus in the year 2472. there he finds an outpost of human colonists living as farmers. the colony is not a success – the land seems unusually poor and recently they are being besieged by representatives of rapacious mining corporations, and more recently, ferocious reptiles. the colony's governor, robert ashe, makes them welcome, and explains the colonists fled a year ago to the planet to escape the overcrowding and pollution on earth.