So it turns out that the Doctor didn't actually need the crystal, but the thing it came in, which he straps to the bus's steering wheel, but it doesn't quite work. Maybe this is also a reference to Donna: "Bus/spaceship, spaceship/bus. I need to weld the two systems together." Maybe this is also a reference to alchemy, in fact: "I need something non-corrosive, something malleable, something ductile, something... Gold." Like the Cup of Hasselbeck or whatever. Christina protests, but he promises he'll be careful with it, and when she finally pulls it out of her backpack the music goes so intensely magical that you might be pardoned for thinking this makes her the new King of England. Then the Doctor bashes the fuck out of it with her hammer, and she's like, "Oi!"
They get it working, and everybody claps like idiots, and they fly through the wormhole, and everybody yells at once, and are shoved around by forces and science, and a couple of the interchangeable people are like, "The bus is flying! He's flying the bus!" in case the others weren't aware, and Malcolm with the gun in his face goes: "I will never surrender. Never." This episode is like the Tritovores: Trying to recycle what better people left behind, but coming up with just sand. I mean, how sad would it be if, having accustomed yourself to eating actual shit, you ended up in a place where there wasn't even shit to eat? Depressing. That's what this is like: The arid ghost of an attempt at eating what was already someone else's full meal.
OMG the flying bus for a million years, and UNIT of course aiming guns at everything, but they don't shoot down the bus, and then the monsters come through behind them, and UNIT blows the hell out of them, and Malcolm shuts down the wormhole, and Christina obligatorily snogs the Doctor while the interchangeables all clap like idiots for like the eighth time, and UNIT takes custody of the interchangeable people to see if they have alien planet viruses and that kind of thing, and Dr. Malcolm runs over and starts humping the Doctor's shin, literally, with the Doctor and UNIT's own Erisa smiling smarmily over his head and having a grudging respect for each other. He tells her he'll do his best to keep their natural manta ray lifecycle off of inhabited worlds, and tells her to hire two of the interchangeables to be in UNIT, and then she pulls the TARDIS out of her ass and there's more applause from all quarters. I'm not kidding.