This impresses the Doctor no end, even though she calls him "Spaceman" and reminds him about Donna, which reminds him about Rose and Martha and Jack and all, Kylie Minogue and Jackson, so he gets sad and standoffish, and takes a moment to discuss with her about how he's an alien with a time machine before finding the stolen Cup of Athelstan, given to the first King of Britain as a coronation gift from Hywel, King of Wales, and nattering at her about being a thief. She thinks he's going to get obnoxious about it, but instead he goes all dreamy and points out that stealing is his lifestyle too, for example his time machine, which he stole from his people to begin with.
Then the beasts start moving around inside the ship, and they try to abandon it, but the flies attack one of the monsters and are dispatched despite being offered a home on Earth by Christina, which is another very Doctor/Companion move. They run around for four million years, and then make it to the bus, where psychic lady helpfully says all psychically, "Run run run run run!" And the Doctor clamps some things to some stuff, to the wheels, and keeps hanging up on Malcolm, who in the midst of much technobabble has discovered a way to close the wormhole, which UNIT's own Erisa wants him to do despite the Doctor almost having saved the bus, and Malcolm can't because he's in love with the Doctor, so he ends up of course with a gun in his face, and this look like, "Shit, I completely forgot I work for UNIT."
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.