Martha likes the library.
Well, maybe like is an understatement. She's always been a reader, and a big fan of libraries. That many books in one place? Pretty damn close to heaven, if you ask her. And the TARDIS library is probably the best she's ever seen, a huge room just filled to the brim with books. It's so big she's not even sure she's seen the entire thing, and she's been exploring it for the past several nights.
It was one of the first places the Doctor showed her, after admitting she wasn't just a passenger and giving her a key. He showed her to her bedroom, the kitchen, and the laundry, and then, with a huge grin on his face, he took her to the library. And she fell in love.
All of the books published up to the early twenty-first century, like in a library at home, would have been enough to keep her busy, except that that's not all. The Doctor told her there are billions of years of human history, after all, and that shows, with the section that's just humanity's contribution to the literary universe. But then there are all the other races and planets, and it makes her dizzy just to think about. Last night she pulled a random book off the shelf, and, once she got over the fact that the TARDIS apparently translated these too, she'd quickly figured out it was a cookbook full of dishes and ingredients she's never heard of, from some place she thinks is called Thexteran. It had pictures, and the food did not look appetizing.
She's been with the Doctor over a week now, and is just coming to understand that while the adventure may be the most overwhelming part of his life, he does have downtime. They've spent the day in the Vortex, the Doctor fixing bits of the TARDIS while Martha kept him company and studied her medical textbooks -- traveling around time and space is absolutely amazing, but she still wants to pick up her life again sometime.
The TARDIS doesn't have nocturnal or diurnal cycles or anything like that, so Martha eats when she feels hungry and goes to bed when she feels tired. She's starting to feel tired now, though, so she bids good night to the Doctor, who's fiddling with the console and his sonic screwdriver. He absently echoes it, focused on what he's doing, and she smiles as she heads to her room. But she doesn't think she can fall asleep right away, so she takes a shower, then decides she might as well do a bit of reading before bed, and goes to grab a book from the library. Their first trip, the Doctor mentioned the seventh Harry Potter book -- Martha grins as she realizes that that's probably in the library as well. She can't wait to find out how the series ends.
She's just heading for the twenty-first-century-Earth section when she sees him, apparently done for now with fixing the TARDIS. He's sitting hunched over a table, several books opened in front of him, scribbling furiously on some paper. It's getting to be a familiar position to find him in, since she's seen him like this every night she's gone to the library, but before, she hadn't been willing to interrupt. But now she's feeling more comfortable with him, and thinks why not as she changes course.
"Doctor?" she asks, tentatively, as she reaches his table. She looks at the books around him, steals a glance at what he's writing, but she can't make heads nor tails of it, even with the TARDIS's translation circuits -- it just looks like a bunch of geometric designs, with a lot of circles. She's seen designs like those before, on the computer in the console room, and figures it's his language. She wants to know what it says, but remembers how like pulling teeth it was just to get him to tell her his planet is gone, and figures that she can ask him later, when they know each other better. She'll leave it, for now.
He doesn't say anything, and she has to repeat his name, a bit louder, before he even seems to notice that she's there. She tries not to be put out about that. "Oh, Martha," he says, blinking. He sets his pencil down and shakes out his hand, as if it's stiff. "I thought you were going to bed."
"I was," she replies, "but I thought I'd just get a book to read first. Then I saw you, and remembered you've been in here for the past few nights, and I was wondering what you were working on."
"It's complicated," he says, rolling his shoulders. "Just something I've been trying to work out for awhile."
"Oh?" she asks, curiosity piqued. "Something you admit you don't know? What is it?"
His mouth quirks in a wry smile, one that seems gently self-mocking. "How to get into parallel universes, actually." There's a flash of emotion in his eyes, deep and dark, but it's gone before she can begin to decipher what it was.
"Parallel universes?" she exclaims, delighted at the thought. "They really exist, then?"
"Oh yes," he assures her, his smile becoming softer. Because of her enthusiasm, she thinks. She can tell that he likes seeing her wonder at everything the universe offers. And he definitely likes lecturing and explaining things, especially to an eager audience. Martha is nothing if not eager, and happily listens. "Every decision we make results in a parallel universe. Most of them eventually collapse back together, since most decisions people make aren't the world-changing kind. But some of them are, and they result in parallel worlds that keep going along their own timelines, completely separate from us in this one. I've even been to a few myself."
"How that, then?" she asks, intrigued. "If you've been to some before, why do you need to work out how to do it?"
His smile dies, and grief glimmers in his eyes. "Never had to do it by myself before," he answers, his voice going slightly distant. "It was easy enough with other Time Lords to help, but now..." He trails off, but she understands.
Then the grief is hidden, and another smile is on his face, a pseudo-happy mask that she's only just starting to learn to see beneath. "What's it for?" she asks, trying to distract him. Make things easier for him by letting him go back into lecture mode. "Did you leave something behind in a parallel universe that you need to pick up, or something?" she jokes.
Except the joke backfires; his mask slips, and the grief in his eyes seems deeper and sharper than ever. He hides it quickly, but she, somewhat disturbed at his reaction, can't quite forget that it was there.
"Something like that," he agrees. "Weren't you looking for a book to read?"
As subject changes go, it's not very subtle, but the depth of the grief she saw is disquieting enough that she's willing to let it go. "Yeah," she says, stepping back. "I thought maybe I'd grab the seventh Harry Potter. You do have it here, right?"
He smiles, but it's not very convincing. "Of course!" he replies. "You want me to get it, or do you think you can find it?"
"I think I can find it, thanks," she says. She starts to walk away, but then, on impulse, she lays a hand on his shoulder and squeezes, trying to give him support. She looks at him until he smiles at her, more genuinely, and then she leaves to find her book.
As she heads back to her room, she thinks about his pain, especially at the idea of something left in a parallel world, and wonders what it could be.
Her first thought is Rose. She doesn't know much about his former companion, but she does know that Rose was important to him, and that she's gone. He put her name between them in Shakespearean England, and sometimes it seems that the Doctor is thinking about her so much that her presence on the TARDIS is tangible, for all that she's not really there. Maybe Rose is in a parallel universe, and the Doctor is trying to figure out how to get back to her.
Martha tries very hard not to feel discouraged at the thought.
He's not necessarily talking about Rose, she reminds herself. Back in New New York, the Face of Boe told him that he's not alone. Maybe there's another Time Lord who was in a parallel universe when the Time War ended, who survived but got trapped, and that's why the Doctor wants to get to one. So that he's no longer the only one of his people left.
It makes sense, especially given the obvious grief he felt at the reminder that the Time Lords were gone and he has to work things out alone. It makes sense, and it's a likely explanation. More likely than that someone from this universe would manage to fall into another one, since apparently multiple Time Lords are needed to even get to other universes. The Doctor said she was with her family, happy, so unless he lied, like when she first brought up his planet...okay, it's definitely time to think about something else. She's really reading too much into this.
But, as she gets into bed, book in hand, she can't quite bring herself to believe it.