When they land in London, Ian and Barbara are happy to be home but celebrations are cut short on realising they’re in the 22nd Century and Earth has been conquered by the Daleks.
The TARDIS materialises, the Doctor surmising from the surroundings that they have landed in London only to find it devastated and in ruins. It turns out the year is some time after 2164. Barbara and Susan are taken by a couple of refugees to a nearby shelter in an abandoned Underground station and meet resistance members named Dortmun (the leader), Carl Tyler, David Campbell, Jenny, Jack Craddock, Thomson, Baker and Larry Madison while the Doctor and Ian stumble across bodies wearing strange metal helmets and soon find an army of them and Daleks rising from the River Thames. The Daleks take the Doctor, Ian and resistance members onboard their saucer and convert any escapees into Robomen.