The Doctor closes the TARDIS door behind him, looking old. Looking tired. He walks to the console, and Rose asks, for the millionth time, "Why her?" But there's no malice here, thanks to Sarah Jane Smith. Just a question, a concern. Some love. "Why did they think they could fix the ship with the head of Madame de Pompadour?" Because she was amazing? Because she was objectively amazing, and because she was composed of the same amount of grace and dirt that Rose is, and you are, and I am. Everyone but the Doctor. "We'll probably never know. There was massive damage in the computer memory base. Probably got confused."
The Doctor taps the console, closing down the time windows now that he's killed all the automatons. Now that he's made those sacrifices worthless. Rose stares at him as he works, brittle and quiet: "Are you all right?" And the Doctor looks up, and says something as incomprehensible, as painful, as ugly, as worthless -- and as true, and as beautiful -- as he's ever said: "I'm always all right." You think he's covering? He's not. He thinks he's covering. He thinks he's being brave; he's not. He's beautiful, and lonely, and exactly what it says on the tin. This is your reminder; you'll only have a hundred more. Oh, sacred be the flesh and blood To which she links a truth divine! The real, unnamed him is this: an angel and a God of Loneliness, and Kindness, and strength. A lonely boy, who learned to worship dancing, but then lost his shoes. A boy who speaks in Estuary Cockney, barely capable of pulling back against all the pain and fear and shame of his last go-round; a boy who has to make this work on his own, alone from even memory. A nearly unchartable, a technically unmappable, labyrinth of corridors, and mirrors, and doors, and gates, and tapestries. And fireplaces. One of which has just gone out forever. One of which has just gone cold.
Rose watches the Doctor softly; Mickey finally figures it out, and tugs on Rose's sleeve: "Come on, Rose. It's time you showed me around the rest of this place." Thank God for Mickey Smith. And though she's timid and though she's hesitant, this is the kind of thing Mickey understands, and Rose knows that -- she's walked his simple halls sufficiently -- and so she goes with him, and shows him the TARDIS: her halls and her mirrors and gates and wardrobes. She glances back, only once -- that's her sin, always; watch -- and the Doctor plays for her benefit, tapping the screen and pulling switches, before they're well and truly gone. He takes out the letter, and begins to read.