Disclaimer: I own nothing except the plot.

A/N: Look - new story! Got the idea a while ago but have only just written it. It's a bit of a change from my usual multi-chapter stories, as it's complete angst/fluff.
It's set somewhere between The Satan Pit and Army of Ghosts, so no spoilers here. Very much Ten/Rose. I'm not really sure how it will turn out. It should be about four/five chapters.
(And thank-you to my friend Maddi for the title inspiration.)
Enjoy!

Snap Decisions

Rose peeked through the library door tentatively, looking behind herself quickly to check that the Doctor wasn't around. Seeing that the coast was clear, she snuck into the musty smelling room, flicked on the light, and headed over to the furthest bookshelf, squinting at the sudden change in lighting. Her light pink dressing gown billowed behind her as she walked briskly across the cold wooden floor.

She stood on the tips of her feet, lifting one leg slightly to give her more height. Her tongue poked out between her teeth as she stretched her right arm up above her head, leaning against the wall of books to steady herself.

Her hand felt along the tops of the books on the shelf it had found, and soon hit a book on its side, just out of view. Rose pawed at the book and jumped up slightly to get a better grip on it. It flew to the ground as she tapped it, along with several others from the shelf, and a cascade of dust.

Rose sneezed involuntarily, and cursed under her breath, looking quickly to the door and freezing as she listened out for any approaching footsteps. After a moment, she decided it was safe, and picked up the books from the floor. She saw the least dusty book - the one she had been looking for - Harry Potter and the Deathly Hallows, and smirked. She was about to replace the other two books on the shelf from which they had fallen when she noticed the title of one of them.

The book in question was fairly large, with a strong black binding and yellowed pages. It was covered in a thick layer of dust, and somehow faded from the sun, and yet the bright golden embossed lettering was still visible. The book looked - if anything - handmade. The calligraphy on the cover was beautiful, though slightly shaky, and it was the only element on the otherwise flawless black binding. Upon closer inspection, Rose found that it read, quite clearly, 'The Companion's Guidebook To Life With The Doctor'.

Her mind buzzing with excitement and confusion, Rose felt her way across to the massive armchair and sat down, curling her legs into her body for warmth. Carefully setting Harry Potter down on the left arm of the chair, she flipped The Companion's Guidebook open to the first page. She found, as she flicked through the pages, that it was a list, and very much like a children's book, with just one point on each page. Returning to the start of the book, Rose got comfortable in her seat, and began to read.

'Welcome, reader. I trust you are a companion of the Doctor. If you are the Doctor, put this book down right now. Please. It's for your own good. Otherwise, read on...' Rose read the words with interest, wondering who had written them so long ago. A sense of disloyalty washed over her as she thought about the Doctor. Would he want her reading this?

She certainly knew her own feelings for the Doctor - and as far as she was concerned, they would stay hidden from him for a while - and she was sure she knew him fairly well too. ('Well, enough to know he doesn't feel the same way.' she thought bitterly.) She knew she didn't need some previous companion's Guidebook to understand him. But then again... just a quick peek couldn't hurt...

She glanced up at the door and grinned, figuring that if she hadn't been caught by now, she was safe for the next few hours. Biting her lip in anticipation, she turned to the first page.

'Number 1: The Doctor is a Time Lord and he comes from Gallifrey. He has a family. It's complicated. Do not question this, as it does not concern you.' Rose immediately felt her expression of glee falter, and she turned the page again.

'Number 2: The Doctor's ship is called the TARDIS. Never regard her as an 'it'. She is the Doctor's 'friend', and is very important to him. Hence, do not be alarmed if he appears to be in love with her. He is not. I hope.

'Number 3: You, the companion, are most likely inferior to the Doctor (unless you are also Gallifreyan, which is practically impossible). He will insult you, especially when he's angry. It will pass, so long as you don't argue. Please, don't argue. He only rants if you do.

'Number 4: Wander off. A lot. If the Doctor leaves you alone, and you do not follow this advice, nothing will get done. Trust me.

'Number 5: It would be better for everyone if you refrained from commenting on the Doctor's outfits/hairstyles/habits/'faults'/glasses/choices of food. No, really. It would.

'Number 6: Do not get romantically involved with the Doctor. It will only end it heartbrake, for both you and him. As he is a Time Lord, he -' Rose slammed the book shut, and it closed with a resounding thud. Not bothering to listen out for any sign of the Doctor, she let the book slip from her fingers and fall to the floor with a second thump.

'What have I done?' she thought to herself worriedly, resting her head in her hands. 'The book's right. It - we - could never happen. He won't let it. And I can't do it to him, not anymore. It's not fair.'

A shiver ran down Rose's spine as she closed her eyes with sadness. Rising silently from the chair, she tucked the two books neatly away on the high shelf and tiptoed out of the room.

Once safely inside her own bedroom, Rose fell onto her bed, feeling like a weight had been dropped on her shoulders. What was she doing?! She couldn't fall in love with the Doctor! It was almost as if she'd only realised this after reading the mysterious Guidebook, though she silently told herself she'd known it from the beginning.

Nevertheless, a thought occurred to her. She'd been holding onto the idea that she and the Doctor would eventually be together, but she couldn't do it. Not to him, or to herself. She'd have to get over him. And if she couldn't do that... she'd have to leave.

- - - - - - -

The Doctor, a few corridors away from the library, was lying fully-clothed on his bed in the darkness of his room, wondering what he could busy himself with whilst Rose was sleeping. He was startled by two thuds followed by the slam of a door, and could only assume that his companion was wandering around in the 'night'. He considered getting up and going to see what she was up to, but decided against it.

Then again... It had happened before. He had heard Rose in the TARDIS kitchen, and gone to see what she was up to. Incidentally, she had been attempting to make a mug of hot chocolate using a frying pan, a blender, and a jar of jam. The Doctor had taken the utensils from her, sat her down, and made her (and himself) a cup of hot chocolate. The travellers had sat at the table and talked for hours, over many cups of hot chocolate, way into the night (although, of course, Time was relative).

Maybe his latest rule about not getting emotionally involved with companions could be slightly... altered. Perhaps. Just a little, to allow him and Rose to...

No, what was he thinking? Of course nothing could happen between him and Rose! He knew how it would end.

But he knew how she felt about him. He had seen the looks, and he certainly wasn't stupid. Maybe he could try. He did like her - of course he did, though to him it sounded so childlike to be thinking such thoughts. But either way, something could happen, if he was to try.

The Doctor made a snap decision. He would.

A/N: A sad start perhaps, but this is a Doctor/Rose story, in spite of what happens in between the beginning and end.

UPDATE: Thank you to NewDrWhoFan for pointing out my mistake about the Time War - it has been corrected.