She doesn't know that I watch her all the time.

I can't help it. If she's in the room, I'm watching. I know that part of it is just looking after her, like I look after everything else. I can't touch something without wanting to fix it, rescue it like some lost kitten. That's how I feel about her. She needs me to rescue her, sometimes from dungeons and chains, sometimes from imminent explosions, sometimes from overzealous suitors, and once, from a dreary, dead-end life as a London shopgirl.

So I watch her, make sure she's happy and relatively safe. (She's with me, so safe is a tricky word to use. But she's still alive, and as long as she doesn't tell her mum about her occasional bumps and bruises, so am I.)

But I can't put it all down to protectiveness. There's something else, too. I catch myself watching for her expressions. It's so easy to read her face. She hates that, sometimes; she's not a very good liar. But I love watching her jaw drop whenever I take her someplace new. She's so full of wonder and excitement; I wish I had half her enthusiasm. And hope; she's absolutely bursting with it. That girl has no notion of defeat. Even when things look to be their worst, somehow, she manages to dredge up some forgotten spark of perseverance. Usually, it's something to do with me. She puts a lot of faith in me, and I'm not quite sure I deserve it. But if it keeps her hoping, I'll just have to make sure I never let her down.

Maybe that's it: I want to live up to what she thinks I am.

I've never had a problem with self-confidence before. If anything, I could probably be described as cocky. But I catch myself watching for her approval. Those smiles she gives me when I've saved the world (again)... Well, they're worth saving the world for. It's so easy to slip into remembering. I've seen so many dead faces, and I can remember them all. So many times I've been just a little too late. So many times, I haven't had a choice. Quite a few times, I've had the choice, and done it anyway. But all it takes is one of those saved-the-world smiles to remind me that I can keep going, no matter what's happened before.

And I will, for as long as she keeps those smiles coming my way. I keep watching for them.

Sometimes, I can't think why I watch her. It's stupid, and I know it's stupid, but I keep doing it. She's just different, somehow. I laugh at all of her corny jokes, and I kill the stray spiders that make her scream (imagine, all she's seen and she can't get over the spiders), and I always make two cups of tea. I've even taken to going with her to do her laundry, just because I miss her when she goes. It wasn't supposed to happen like this. I know that, even though I'm not quite sure what happened. Somehow, she just slipped into my life like she always belonged there. Every time I turn around, there she is, trying to nick the sonic screwdriver, telling me when I'm being rude, or complaining that the bomb stains are never going to come out of my jacket.

The funny thing is I kind of like it.

She falls asleep like this, sometimes, draped over me like I'm actually part of the sofa. She insists that she loves it when I read to her, and Harry Potter is pretty exciting for late-night reading, but when she nestles into me like that, I know she's going to sleep. Afghan wrapped around her, she looks small in the firelight. She's beautiful; she's mine.

And she has no idea. Maybe she will, one day.

I keep watching.