The TARDIS by the Thames

The TARDIS materialises near a rubble strewn plot of wasteland alongside a very dirty looking river. On exiting the TARDIS The Doctor surmises from their surroundings that they have landed in London. This news delights Barbara Wright and Ian Chesterton as it looks as if they have at last managed to return home.

But something is not quite right. It is curiously silent and London looks deserted. They also notice the look of decay around them making The Doctor wonder about what year it is, fearing that it is nowhere near Barbara and Ian's time. Susan attempts to see if she can see anything of interest but in doing so she slips on the loose rubble and twists her ankle. At the same time the bridge, under which the TARDIS has materialised, collapses, so burying the TARDIS and blocking the travellers' access to it.

While The Doctor and Ian Chesterton go off to a nearby warehouse to look for some tools, to help them shift the rubble away from the TARDIS door, Barbara remains behind to look after Susan. In the abandoned warehouse, The Doctor and Ian are unaware they are being watched. They also find a calendar marked 2164 – proving that they have arrived in the 22nd-century and so nowhere near the time Barbara and Ian started travelling in the TARDIS.

Back on Earth

However, when The Doctor and Ian return to the where the TARDIS landed there is no sight of either of the two girls. Unbeknown to them Barbara and Susan have meet up with a team of resistance fighters, led by the wheelchair-bound Dortmun who informs them that Dalek invaders are now ruling the Earth with the aid of some humans who they have converted into zombie-like Robomen.

The Doctor and Ian also become aware of this fact when they are captured and taken to a Dalek saucer. But they are soon rescued before being turned into Robomen. The Doctor is subsequently reunited with Susan and meets David Campbell a young man with whom she has become friendly with.

A Dalek Emerges from the Thames

The Doctor learns that the Daleks have established a huge mine in Bedfordshire and that they intend to remove the Earth's core using a huge bomb and replace it with a powerful drive system so that they can pilot the planet around the galaxy.

Even though The Doctor is rescued in the resistance fighter's attack on the Dalek's saucer Ian though is unable to escape and so is left onboard the Dalek saucer when it takes off and so finds himself hitching a lift to the Dalek mine in Bedfordshire.

Dortmun has meanwhile persuaded Barbara and a young resistance fighter to travel with him but his obsession with the success of his bombs eventually leads him to make a suicidal attack on a Dalek patrol. Barbara and Jenny manage to escape and so also decide to head for Bedfordshire.

The Dalek Saucer Over London

There The Doctor and his companions finally meet up and together they are able to thwart the Dalek's plan. Ian manages to create a barrier in a mine shaft in order to intercept the bomb. The resulting explosion creates a huge volcanic eruption which destroys the Daleks, their saucer and the mine.

On returning to London, to be reunited with the TARDIS, The Doctor realises that Susan has fallen in love with resistance fighter David Campbell, and so locks the TARDIS doors to prevent her from entering. Despite the heartache it causes he realises that it is best to leave her on Earth to find a new life with David, while he continues on his travels with Barbara and Ian.

As Susan looks forlornly at the empty space where the TARDIS used to be, she fingers the TARDIS key on the chain around her neck. David reaches his hand out to her and she takes it, dropping the key onto the ground as they both walk away to start their new life together.