So the Doctor and Malcolm nuzzle and lick each other's science for awhile and then the Doctor hangs up on him, and the aliens are still angrily poking at their screen and clicking and burping at them, and the Doctor takes pictures of the oncoming storm, which in case you didn't catch that one, the magical lady goes, "So fast and strong, they ride the storm. They are the storm. They devour!" And meanwhile, the Doctor and Christina are taken prisoner by the clicking-burping people, who are humanoids with the faces and segmented eyes of your common housefly. Inside their ship, it's very cold because of made up metal that does that, gets colder the hotter it is, and the Doctor goes, "Since I met you, Christina, we've been through all the extremes!" and she goes, "That's how I like things. Extreme!" and you just want to punch them both in the throat.
So there's a whole miscommunication where of course Christina assumes that these folks had something to do with their being pulled through the wormhole, and the folks themselves assume that the bus and its associated interchangeable assholes had something to do with their spaceship crashing. But of course neither of these things is true, because there's the oncoming storm that did both. The Doctor acts generally embarrassing and explains that the people -- "Tritovores," as in detritus, right, because Rowling is just the best we can do -- are having spaceship trouble, which the Doctor self-congratulatingly kicks back into operation.
While their civilian charges are frying in the desert with actual psychic-verified death flying at their boiling faces, the Doctor and Christina kick back in an air-conditioned spaceship and watch a movie. The Tritovores, the movie and the unending clicking explain, were traveling here to Sanhelios to trade their wares for, um, shit, because they are flies, but when they got here it was just sand, even where they are chilling out, which used to be the capital city of the whole planet, but is not also sand. Sand, the Doctor explains, made up of city and oceans and mountains and wildlife and 100 billion dead people. Christina wigs out because that means she's got dead folks in her hair, because women are so flighty about that kind of thing, especially if their parents have money, and isn't that hilarious: "Something destroyed the whole of Sanhelios," he goes, and she's like, "Yes, but in my hair!" You know who acts like this? Fucking nobody real.