The fire, as it turned out, was not on the sofa or in the skull. It was crackling merrily in the hearth, much to John's surprise and elation. He was not too sure what was actually burning, but didn't feel inclined to find out. It was probably the books belonging to Sherlock that make the fireplace their home. In John's opinion, Sherlock had far too many books cluttering up the place. He could afford to lose a few.

The three of them; ex-army doctor, consulting detective and pyromaniac punk, were sitting around the fire. John was in his armchair, talking to Snow. She was sitting as close to the fire as he would let her, and staring with transfixed fascination at the flames. He talked cheerfully, updating her about how Harry was and what he'd been getting up to. She answered his questions fully and asked some in turn, but she did so without animation or emotion. She didn't look at John. She was completely absorbed in the flames. Every so often her hand would, seemingly of its own accord, gravitate toward the blaze, reaching out towards it. A sharp 'Snow!' from John was enough to return the hand to her side, but her eyes never left the crackling fire.

So when Sherlock softly called 'Caitlin', he was almost shocked when her eyes immediately darted up to meet his gaze. John carried on talking to her, having neither heard nor noticed his flatmate.

'Yes?' Caitlin prompted when John's steady stream of mundane chatter had finally petered away.

'Snow. Not derived from Caitlin, is it?' Sherlock held her gaze steadily from his superior position on the sofa.

'Nope,' she confirmed, popping the 'p'. She offered no more information, even when Sherlock's stare turned questioning. With a resigned sigh, he asked;

'So where did it come from, then?'

And suddenly Snow was on her feet, and then only on one foot as she twirled in an expert high-kick directed at John's surprised face. It was the kind of spontaneous combat manoeuvre that John knew to expect, and that Sherlock would soon learn to. John expertly caught Snow's foot an inch before impact, and with a sigh pushed her away. John's weary gesture told Sherlock to anticipate many similar playful fights.

With her foot still pointed aggressively at her relative's face, Snow started to explain. Her tone was teasing. 'It's all this ol' fool's fault. He decided to misinterpret my words-'

'Misinterpret your words! I asked you your name and your said 'Snow'. Don't blame this one on me.'

'I was five!'

'You understood the question.'

'I chose not to answer.'

'No, you chose to answer wrongly.'

Another spinning kick was directed at John, and blocked easily. Sherlock was quickly becoming bored of the argument, which had obviously been staged so many times that it was almost scripted. He held up a hand to stop them.

He was ignored.

'You already knew my name! Mother would have told you when she sent you to look after me!'

'No reason to ignore a perfectly reasonable request. It wouldn't have taxed you to say 'Caitlin', before you continued on with your frantically idiotic-

'IDIOTIC! I am not idiotic.'

'You wanted to know if it was going to snow! It was July!'

'I LIKE THE SNOW.'

And with that, the riled teenage drama queen turned and with a flick of her waist length hair flounced out of the room and up the stairs to John's bedroom. The two men heard the door slam. Neither wondered how she knew where it was.

After a few moments of awkward silence, John turned sheepishly towards Sherlock. The consulting detective was reclining on the couch and facing away from the doctor. John had no idea that he was smirking.

'Sherlock?' John encouraged tentatively. 'I'm so sorry about her. Really. She's a bit of a handful. Okay, she's a lot of a handful. But her mind's brilliant, like yours. She's a sister to me, Sherlock.' John's voice, which had started out at a playful tone, had turned pleading.

'I know that. What are you trying to persuade me of?' Sherlock knew that John was 'subtly' asking if the girl could stay. Sherlock also knew why she needed to. Sherlock wasn't sure if he wanted her in the flat.

'Look, Sherlock, I know this is really sudden. I know you're not a fan of people-'

'Pah.'

'Snow does this. To me. A lot. Too much. She turns up on the doorstep, or in the house... Actually, it's always in the house. And she stays with me for a while. Because she's got nowhere else to go. Sherlock, right now, that girl has nowhere to go.'

'I know.'

'Of course you do. And you know why. Why do I bother to tell you anything?' John sighed, worn out. He seemed almost defeated. Sherlock rolled over slowly to face his friend. John had his head in his hands. He thinks I'm going to refuse the girl, Sherlock realised with surprise. He thinks I hate company that much. He thinks her past would scare me. Not likely.

'She can stay.' Sherlock's voice was carefully bored sounding.

'What?' John's head shot up.

'You heard me. I'm going to my room. I'm in the middle of a particularly tedious but necessary experiment. 'Snow' will be down in... a few minutes. Wearing one of your shirts, if I'm not mistaken. You should really see to her back.' Then Sherlock turned his back on his flatmate and stalked off to his room.

John couldn't help but draw parallels.