If she never sees another library again, Donna thinks, it will be too soon.

It's been a week – or thereabouts, anyway, it's not like there's proper time on board Mr. Toad's Wild Ride – and she hasn't shaken it yet. She leaves the lights on when she sleeps. If they're anywhere near children Donna heads the other way, and fast. Sometimes she dreams of a man with a stutter, and the weirdest bit is waking up and remembering he'd been a dream in the first place.

She sinks into the jump seat while the Doctor fiddles with the controls. It figures, she supposes. Probably she should've known. The universe seems to be pretty dead-set against Donna Noble getting hitched.

"You're quiet," the Doctor observes, peering around the time rotor to look at her. "You okay?"

How the tables have turned, Mr. Bond, she thinks but doesn't say. Instead she only nods. "Yeah."

The Doctor is silent another moment, still flicking switches and hitting buttons. Recalibrating the something-or-other, he'd said. Sometimes Donna wonders if he's really doing anything at all, or if he's merely incapable of standing still.

Then he looks back up at her.

"Lee?" is all he asks.

Donna smiles sadly and nods again. "Yeah."

He frowns at her sympathetically. The concern in his expression is one she's seen a fair few times more than she'd like to admit. "I'm sorry you didn't find him."

"S'all right. Should've known he was too good to be true." She shrugs, because there's nothing else to do. "And if he was real – what then? 'Oh, hello, we were married in a virtual reality, remember me? I'm from 21st century Earth, this is the alien I travel time and space with, hope you're all right with a long distance relationship, we'll pop by and see you every few years, how's that sound?'" She snorts. "Not exactly conducive to good relationships, is it, this life?"

One corner of the Doctor's mouth tilts up in a grim smile. "No, I suppose not."

He returns to circling the console, occasionally pausing to rotate a dial or pull a lever, and Donna considers what she's just said. Not exactly conducive to good relationships. She'd known that, always known that, from the instant she stepped on board as a passenger rather than a reluctant abduct-ee. At the time it had seemed a worthy sacrifice, trading in awkward first dates and inevitable breakups for seeing the vast reaches of the universe. Being nearly fed to a giant alien spider by her supposed fiancé had left Donna wary, to say the least, and she'd written off that aspect of her life the instant she'd decided to find the Doctor.

And then came the library.

She doesn't regret her choice, and she doubts she ever will – still, she thinks of Martha and her wedding ring and wonders what might have happened if Lee had been real, after all.

"You can leave whenever you like, you know," the Doctor says, startling Donna out of her trance.

"What?" She narrows her eyes suspiciously. "Do you want me gone?"

He keeps his back to her and speaks with a casualness she doesn't quite believe. "No! I just mean – if you ever wanted to –" He shrugs. "You could leave, is all. Your choice."

Donna stares incredulously. "What, you mean if I want to swan off and shack up with some alien bloke that's fine by you?"

He moves around the console and gives her a wry grin. "Wouldn't be the first time."

Donna snorts. "Well, don't count on it. You're stuck with me forever, Spaceman."

The Doctor flinches, and Donna thinks suddenly of the woman from the library and her diary full of "spoilers". You're Donna Noble? she'd said, like it was something important, and even remembering the words puts Donna on edge. River and Martha, they'd said the same thing, hadn't they?

Donna plans to spend the rest of her life in this impossible blue box, traveling with the half-mad alien in front of her. Perhaps the universe has plans of its own.

"Almost done," the Doctor says, tapping something out on the TARDIS keyboard. "Shouldn't be much—"

"What happened to Rose?"

She asks because she's curious. She asks because she doesn't know what lost really means. She asks because she remembers the crack in his voice when he'd said the girl's name, and she asks because maybe the universe had its own plans for Rose, too.

His fingers still, hovering above the keyboard. "What?"

"Rose," Donna says – gently, because she sees the tension in his posture, like a deer caught in headlights. "Where is she now?"

For a moment he looks as though he hasn't heard her; then he jolts and plasters a grin on his face as he turns to face her. "Right, Rose! With her family. Parallel world."

Donna frowns. "She's from a parallel world?"

The Doctor's unconvincing smile dims a few degrees. "Well, not originally, no." Without warning the smile comes back full-force. "But that's where they are now, Rose and her mum and her sort-of father and her… Mickey. The whole Tyler clan!"

"Right." She nods, and she wonders when she first began to tell the difference between his happy smiles and his sad ones. "And how'd she end up there?"

"You remember the Cybermen?" he asks, and Donna nods, though she doesn't so much remember them as she remembers researching them after the wedding that wasn't. "They came through from that parallel world. We had to close the gap. When we did, she…" He hesitates, and once again for just a second the mask slips. "Well, she was on the other side."

The mysterious Rose, Donna thinks. The one he'd lost, the one who'd trusted him, the one he'd spent Christmas with, the one whose name he'd practically choked out. They'd been different people that day, her and the Doctor, and in the months that had followed Donna had spent a lot of time wondering what kind of woman could bring a frightening alien so close to tears.

Donna doesn't know what to say.

The Doctor doesn't give her time to think of something. He waves a hand and turns back to the console, staring at the screen. "Still! All for the best. They're all together this way. Safe. One big happy family!"

One big happy family. She thinks of Jenny – of Martha's warning – of lost all that a long time ago – of her father's funeral – of children who never existed – of my friend, she had this family.

She sighs, and she wraps her arms around her middle.

"Couldn't we go and see her, though?" She gestures upwards with her head. "This thing goes anywhere, doesn't it?"

He shakes his head, his smile rueful now. "No. Parallel worlds are closed off. When my people were still around – well, anyway, they're closed off now. Breaking through would be a bad idea, with a capital 'bad'."

Once more, Donna nods. How frustrating it must be for him, she thinks, to have all of time and space at his fingertips and yet be shackled to a universe without Rose.

"You two were…?"

The Doctor says nothing. Donna supposes that's the closest she'll get to a confession.

"You miss her." It isn't a question.

He swallows. His knuckles have gone white as his hands grip the edge of the console. He stares at the screen and inclines his head in an almost imperceptible nod.

"Yes."

One word, and she wants to hug him. Instead, she curls her arms tighter around herself. "I'm sorry."

The Doctor pushes himself away from the console, turns and shoves his hands in his pockets. "Don't be. I'm fine." He grins. "And Rose – oh, she's fantastic. Might even have her own family, don't know how long it's been, time runs differently over there. She's probably forgotten all about me by now."

Donna snorts, and one eyebrow rises of its own accord. "I doubt that. Not exactly an easy bloke to forget, are you?"

"She's happy, Donna," he insists, conviction in his voice, the smile gone from his face. "She doesn't need me."

He sounds desperate, as though Donna's belief in Rose's happiness is absolutely imperative to the functioning of the universe. Donna wonders if they're still talking about Rose.

"Of course she is," she says gently.

The Doctor nods once and turns on his heels to stare at the monitor, his hands still firmly wedged in his pockets, his shoulders still tensed. Donna rises to stand next to him. They look at each other, and for once there are no masks at all.

The Time Lord who lost his love to a parallel universe and the woman who'd invented hers. God, what a pair, she thinks. Laverne and Shirley. Thelma and Louise.

One corner of her mouth lifts into something like a smile. "You still owe me a beach."

"I'm not really one for beaches," the Doctor admits. Then his face lights up, and this time she knows it's genuine. "Ohhh, I know just the place, Donna Noble! How do you feel about a leisure palace on a planet made entirely of diamond sound?"