The Doctor is abducted to a desert planet, along with a busful of stereotypes and a tragically horrible young aristocrat named Christina. While it's natural to despise her, we would be remiss if we didn't also note that she makes a great Companion to His Yippiness -- but the Doctor will have none of that, continuing the post-Donna theme of darkness and loneliness and general whiny wound-licking.
Turns out it's not so much dust all over the place as it is the digested remains of an entire planet, thanks to wormhole-travelling nightmare manta ray-looking metallic creatures. They showed up, ate the planet and all its inhabitants, and are now spinning a wormhole that will take them to Earth.
Christina and the Doctor team up with some giant-housefly aliens to disarm the creatures, while back on Earth UNIT begins taking Harriet-type steps to eradicate the threat altogether. Man, Martha turns her head for five seconds and the whole place goes predictably apeshit. Luckily, UNIT don't have to block the doorway, as Christina's cat-burglar skills and general Mary Sueness help the Doctor pull out a last-minute victory.
The Doctor takes a good ten seconds deciding to ditch Christina, hooks a couple of the stereotypes up with UNIT jobs, and takes off... But not before a psychic warning from a Magical Black Lady tells him what we've already known for some time: He's not going to last much longer.
It's nighttime in the International Gallery, and with great precision a bunch of police or security guys stand all around this one exhibit, a gold cup of some kind, which is also guarded by lasers. So there's five guards, plus lasers, because that's how important this thing is, but of course the cupola directly above the exhibit is removable, and some kind of ninja comes down on wires and steals the cup from above, and then zips back up into the sky. A confusing mix of due diligence and weird loopholes they've got going at this gallery, but then, a confusing mix of due diligence and lazy-ass bullshittery is this episode.
So then there's one of those lucky happy kitties waving at a guard, and he pulls the alarm, and on some other level the ninja takes off her mask and prepares to have herself a big old smugfest, but before she can clap herself on the back for the first of many, many obnoxious times she'll be doing so, she has to run for it! Then outside, they're arresting her partner, so she smugs, "Sorry, lover!" and runs off in the other direction, which infuriates some nameless cop dude we never actually get to know or care about whatsoever, who is some kind of detective who is obsessed with tracking this asshole down, but we have to find that out from context because, like much else about this episode, characterization is phoned in to a degree we did not know what possible until now.
A bus pulls up and the thief is like, "I don't have a paying device! What is 'money'?" because she's aristocratic and all, and gives the driver her diamond earrings, because she's so rushed, and then the Doctor gets on by psychic-papering the card-reader, and then he's like, "Everybody on this bus is paper-thin and irritating, but which one's scorchingly obnoxious enough to take eyes off my own scenery-chewing? Which person here is the most like rubbing sandpaper on an infant's skin whenever she opens her fucking mouth? Because that will be my BFF."
So the Doctor sits down next to her and starts babbling, like he does, and gives her his chocolate orange and has some irritating science fiction device that he woggles about and yells at for awhile, and all the idiots on the bus stare at him because blimey isn't he strange, and then the nameless asshole cop somehow manages to cordon off both sides of this tunnel in order to cage the history thief, but the Doctor locates some "Rhondium particles," and then the little satellite dish on his thing starts going around, and shoots sparks at this irritating older lady, and he apologizes -- "Sorry, that was my little dish!" -- and then he tells everybody, including the ninja who is named Christina, to hold on tight. Some irritating/cute kid comes flying out of the WC, and then they go through a wormhole.