You Are Not Alone
The Doctor's like fire and ice, and rage. He's like the night and the storm, and the heart of the sun: he's ancient, and forever. He burns at the center of time, and he can see the turn of the universe. He is terrible. He has two hearts, and one of them is broken, so the other one's beating twice as hard. You're a god, riding with angels: who's going to stop you? Know your enemy: that's grace, hiding and waiting to jump. And know your archangels: they're the ones bearing their double-edged swords, guarding the Garden, keeping you sane and able to grow. The Empress teleports away, back to her ship, but a Mr. Saxon orders her ship destroyed, and so it is. The Earth is defended. The Thames is dry.
Donna refuses to go on traveling with the Doctor: he's terrifying, he burns at the center of so much danger and chaos. This is not a job for a grown woman, even if Donna and the Doctor are so completely in the same situation no matter how you cut it. No matter how high/low culture you cut them, no matter how Heaven/Earth the division between them, she's the only person who can really understand what he's going through: to be the last of something you thought made up what you are. To go from being a part of the forest to being just a tree: and watching your forest bite you in the ass. And still, Donna makes a stronger choice than the Doctor does. But he does need somebody, she knows that much -- when the god's heart leaves his man's heart too far behind; when that heart beats too loudly for him to hear anything else. He needs somebody to stop him, when his need to master takes him too far. Donna Noble asks her name, the Companion he lost, and finally: "Her name was Rose," he says, datum pacem. And then he's gone.
III: Smith & Jones
We get another echo of that heartache in the first proper Martha story: a little sweet old lady turns out wrong, and the terrifyingly awesome Judoon turn out...well, not sweetness and light, but respectable, certainly. Much is made of genetic transfer, blood drinking, what's human and what's not. There's a theme for you: another woman older than time, who can't be stopped. Another nuclear secret inside what should be sweet; another dose of horror inside a simple cup.
When the Doctor appears in the hospital, sparks flying, weird time loops abounding, he's only got one working heart. Which one do you think it is? Martha CPRs the Doctor's two hearts and revives him. She remembers to work both sides, god and man: she gets them both beating again, and he saves the world. His human heart is put not in Donna's hands -- whatever she thinks, this isn't a love story -- but into her care, for the remainder. She is the shepherd of his humanity; sometimes literally. Who better to take charge of one heart? A doctor that doctors Doctors. Who better, to heal a god, or an angel, or Albion? And tonight, Donna agrees to the Doctor's petulant offer of a reward trip, into the past; he lies right to her face and through his lovely teeth about how he prefers to travel "on [his] own," and when she asks if he ever had a brother, he says he doesn't. Not anymore.