When the Doctor enters, dressed as a Santa, the Empress of the Rachnoss immediately sees through the disguise, of course: you can't do seemings in front of stuff from the depths. They're about the ugly truth, about teeth and blood; they don't have the imagination to be fooled. The Doctor makes the Empress an offer: he'll find a planet for her and her children, if she ends it. If she and her children give up their birthright, if they agree to give up what is theirs, he will relent. But shadows can't grow brighter by the shouting of the light, so the Empress declines. What happens next is her own doing, the Doctor impresses upon her, and he tells her his world. It is far away and long since gone, but its name lives on. Gallifrey. Unspoken Gallifrey, silver-leafed trees and burnt orange sky, deep red grass. Gallifrey, the shining world of the Seven Systems. Gallifrey of the Untempered Schism. Gallifrey, the murderers of the Rachnoss. The Empress screams in rage and fear, the oldest enemy back again, killing her children. The Doctor takes some ornament bombs and tosses them into the walls and pipes, bringing the river into the base, into the pit. The room is full of fire and flood, and the Empress screams. Donna begs him to stop, tries to give him peace, but there's no peace here. Just rage. Rage, because there's one planet in all places and times that brings him back, that gives him peace and makes him feel something. Now that Gallifrey's gone, it's home. And at the center of that planet, it turns out, is a secret. Something dark and scary, something forgotten, something you can't wrap your head around because you don't have enough information. If I give you something that looks like this
what you're seeing is two dots and a curved line. But you're turning it human. You're reacting to what's in front of you, and there's no harm in that, but you can't forget that you're the one doing the work. Taking a god and falling in love with him. And he's just as guilty: there's a reason they call it the arachnid reaction -- where the dots and line stay that, or turn into something worse, because you can't stand looking at something so alien as a spider or a scorpion, or a Rachnoss Empress. This is a betrayal by Earth herself, to reveal something like this at her center. To break apart the wish in front of him, after he's lost so much, and show him how horrible everything can be. How even a lonely god can have his heart broken.
Look out for the fixed points: they're anathema. The Doctor stands or dances in the heart of the storm and it turns about him. Jack is a fixed place. Rose was a fixed place, the part that kept him grounded, connected to the center. And she turned into spider babies and broke his heart. Earth full of spider babies is isomorphic to the Doctor and Rose stupidly promising they'd make it work this time: it breaks apart and bites the Doctor in the narrow ass. But Earth is also home, and he's never been good at seeing the dark side of things, so it must be the Empress that's the problem. It's not that one heart is broken, locked up on the other side of the Void; it's not that the other heart is beating twice as hard and fast. It's not that he's raging; it's just that somebody won't leave Earth alone. And luckily, he's a god. He can handle it. He can master her.