The TARDIS materializes in 22nd Century London, but the city is devastated and in ruins. A quake buries the TARDIS and the time-travellers cannot leave. The Doctor and Ian explore, but Susan and Barbara are taken by refugees to a shelter in an abandoned Underground station, where they meet the human Resistance. The Doctor and Ian stumble across the Resistance as well, and see, in a memorable scene, a Dalek rising from the River Thames. They learn that the Daleks invaded Earth following a meteorite strike and a plague. The Daleks kidnap The Doctor intending to turn him into a Roboman as they do with captured resistance fighters.
The Daleks are attempting to hollow out Earth's core so they can pilot the planet through space. To stop them, the resistance must travel to a mine in Bedfordshire where the project is taking place. Ian, hiding in the Dalek saucer, is taken there, while the others are involved in rescuing The Doctor, attacking the Daleks in London, and stopping their attempt to raze the city with firebombs, and then they head off for the mine. Susan is starting to fall in love with David (Peter Fraser) a handsome resistance fighter.
After a battle with the Slyther, the monstrous pet of the Black Dalek, Ian ends up at the bottom of the mine, collaborators turn Barbara in to the Daleks, and they face other cliff-hangers before destroying the Daleks in a volcanic eruption. Back in London, the TARDIS is freed, and David asks Susan to stay, marry him, and help rebuild Earth. Before she can make this agonizing decision, The Doctor, who knows what is going on, vanishes with the Tardis.
This was the first Doctor Who story that used extensive location filming. The scenes of Daleks trundling through the empty streets of London--Whitehall, Trafalgar Square, Westminster Bridge, the Royal Albert Hall, etc.--were very effective. The poor actors trapped in the Dalek contraptions all day learned that they could pee into the city storm-drains and there was a long line of Daleks waiting to use them. Carole Ann Ford wanted out of the Susan Foreman role because it had never become what she was promised. She wanted scenes of daring-do to take advantage of her gymnastics skills, proposed telepathic powers that were only hinted at, and lots of gorgeous Sixties costumes. Instead, she was almost always just a terrified girl. She should have known better when she was asked to scream during her audition.
The serial resulted in two big-screen movies: Dr. Who and the Daleks in 1965, with Peter Cushing as The Doctor and Roberta Tovey as Susan, which was largely based on The Daleks--the first story in which the Daleks appeared--and The Daleks' Invasion of Earth: 2150 AD, also with Peter Cushing and Roberta Tovey. These movies are not considered canon. For one thing, The Doctor is a human being from Earth and for another he is called Doctor Who and The TARDIS is called simply Tardis. The interior of the ship is quite different from the one on TV. Most egregious of all--unless you count the Sugar Puffs product placement--it uses music written by Barry Gray (the composer for Gerry Anderson's Super-Marionation series--and not the beloved Doctor Who theme by Ron Grainer. It's like Never Say Never Again, which is a good movie, but you miss the James Bond theme.