The Doctor tells Martha that her one trip is over, and she can go home now... unless she wants to travel more. No reason, really, he'd just like to travel more. In fact, he'd like to take her to the future: New New New, etc., York. Where drugs are cheap, legal, and socially acceptable. Where people inexplicably look like cats. Where traffic never moves.
Where the Doctor also took Rose once.
The Doctor even tries to make the same little jokes he made to Rose when he first took her there, but they just don't work as well when Rose isn't around to hear them. By now, Martha's figured out that she's the Doctor's "rebound", and she doesn't like it one bit. Also, the TARDIS has taken them to the undercity slums, where things aren't quite as happy as they are above the smog.
Martha gets kidnapped by the ghost chick from
Being Human so that her kidnappers can have enough people in the car to get access to the elusive carpool lane. The Doctor chases after her... into the Traffic Jam From Hell.
Before he dies of extreme toxic smoke inhalation, though, he gets picked up by
Cat Folk Thomas Kinkaide Brannigan (who looks like
Father Dougal as a cat-person) and his wife Valerie. Estimated time of arrival? Oh, another six years or so.
Screw
that. The Doctor jumps from car to car, and tries climbing down to Martha's spot, but he can only get so far.
Meanwhile,
giant evil crabs that feed off pollution have snatched Martha's car out of the air and are hell-bent on eating her. The Doctor quickly recognises them from an old
Missing Episode and notes that they've devolved into mindless beasts over time, living in the depths of the expressway. Even if he could get there, there's hardly any way to get back.
The Doctor will not be deterred. He gets into the upper city, where the only remaining "people" are an
elderly cat nun and the Face of Boe, the oldest being in the galaxy, who is the only thing powering the expressway and keeping the rest of demi-humanity alive. It turns out that the planet's inhabitants all got addicted to the drugs, causing them to waste away in drugged-out bliss... and then the drugs produced an unstoppable plague that killed everyone (including itself). And all the expressways are closed, and have been closed for years. All those cars with all their eternal fuel and food supplies are driving in eternal circles around the deadly city smog.
The quarantine placed on the planet was set to last 100 years, so it has to be released manually. The Face gives his life to open up the expressway exits and save Martha. The Doctor opens the gates of... well, Heaven, and all the cars ascend into the bright upper city, with the people inside praising Jehova for saving them from the crabs of... well, Hell. They sing hymns and everything. This planet really sets off the Doctor's messianic side, after that whole "getting baptised by nuns with a panacea and curing all the lepers with a single touch" thing he did last time.
As Face dies, he imparts his final message, as foreshadowed in "
New Earth". The message? "
You are not alone."
Martha refuses to leave until the Doctor tells her just what he is and what's going on. The Doctor sits down with her and tells his story from the beginning, starting with "there was a war"...
Tropes
