Lestrade was singing. Normally, Sherlock wouldn't have minded. He never said anything on the rare occasions that Greg deigned to sing, and he certainly never would have corrected his ever-constant botching of the lyrics, but this time... well, this time was just a bit different.

"Deck the halls with bells of holly..."

"Boughs," Sherlock growled.

"Sorry?" Lestrade stopped mid-stride, a coffee cup clutched in one hand and a thick loop of shiny, white garland in the other.

"Boughs of holly."

"That's what I said."

Frowning, Sherlock looked up from his laptop. "You said bells. Bells of holly doesn't make any sense."

"Huh." Lestrade set his cup down on a side table and dropped the garland on an adjacent armchair. "I've always sung it that way. Nobody ever said anything." He shrugged, kneeling to assemble the final pieces of a false Christmas tree he had insisted upon putting up in Sherlock's dingy flat because the place was too 'gloomy'. "Maybe the holly is arranged in a sort of bell shape, y'know? Like those little mistletoe branches that you hang from the ceiling."

Clearly perplexed and perhaps slightly annoyed, Sherlock shut his laptop and turned to face the DI, the soft fabric of his dressing gown rasping quietly against the upholstery as he did.

"You know what I mean," the DI went on, noting Sherlock's confusion and waving it away. He snapped the last piece of the tree together and stood it up. "Doesn't matter anyway, I s'pose. Nobody nails holly up on the walls."

"It's a bit archaic, yes... Why exactly are you, er, decking my halls?"

Greg shrugged. "Donno. Just seemed inappropriate not to have something."

"Have you ever known me to have a Christmas tree?" Sherlock challenged, picking up his violin from the coffee table. He lay back on the couch, the laptop carelessly discarded on the floor in favour of his rather unmusical pizzicato.

"No, and it just isn't right. Didn't you celebrate Christmas when you were growing up? You must have had a Christmas tree." He sifted through the decorations at his feet and clicked his tongue. "Forgot the fairy lights."

"No fairy lights."

"Fine then."

"And yes."

Lestrade glanced over.

"Yes, we did celebrate Christmas," Sherlock continued, picking distractedly at the violin strings. "But it was a dull, dismal affair."

"What? Why?" Greg had begun stringing garland round the tree, stepping over Sherlock's clutter and his own piles of ornaments alike.

Shrugging, Sherlock abandoned the violin on the side table and picked his way over to the tree. He stood on the other side of it from the DI and took the shining loop of garland, wrapping it round his side before handing it back. "All the fighting," he said at last.

Lestrade wound garland across his side, unable to see Sherlock except for the long, thin hand that reached around the tree to pull the excess across. "Fighting?"

"You've met Mycroft. Hurry up over there." His fingers twitched impatiently until Lestrade placed the sparkly loop into them. "We never got on. You wouldn't believe how it upset our mother. Which upset our father. Who shouted. Which upset everyone even more. As I said: dull. Dismal."

"Well, it isn't supposed to be that way. I mean, you know that, right?"

Sherlock shrugged, but Lestrade didn't see it.

"Sherlock?" Lestrade peered at him from between a pair of false branches. "You do know that?"

"What was it like for you?"

"Christmas? It was nice." The DI smiled warmly. "My sister and I always woke up early on Christmas morning. Mum and Dad would have been up all night wrapping and labelling gifts for us all, and arranging them all nicely round the tree. So our favourite thing was to wake up before them and go down to see everything all set up neatly. We would sit on the stairs and just look at it, wondering which ones were for us. I mean - there was never much, but to us, at the time... it was the most amazing thing." He paused long enough to stick the end of the garland in the back where it wouldn't be noticed, and popped open a box of little metallic bulbs, shoving it under the tree toward Sherlock. "Here, start putting hooks on these."

"And then?"

"And then hang them?"

"No - Christmas. You were saying." Sherlock's nose and eyes peeked round the boughs of the tree for just a moment before they disappeared again. Shortly, he thrust a newly-hooked bulb out at Lestrade.

"Oh. Um. Well, then our parents would get up and we'd all sit and open presents. It was the first thing we did once everyone was awake. My mum always insisted on video taping the whole affair. We never watched the tapes, though, never. I think we all forgot about them. So anyway we'd open presents, and then my dad would make this huge breakfast. In the evenings we'd have this really lavish - well, lavish for us - dinner and watch one of my mum's old Christmas films." He shrugged. "I guess we had a bit of a tradition like that."

"Mm." Sherlock nodded slowly, absorbing the DI's words as he hung a shining blue bulb on one of the highest branches. "And now?"

"Well... now my mum's gone and my father lives in Dorset, and my sister has her own family..." He shrugged, but there was nothing close to indifference in his voice. There was an ache there that went unmarked and untold.

And against all odds, it was Sherlock who spotted it.

"Now you spend Christmas with me," the detective offered nonchalantly.

"Hmm?" Lestrade peered round the tree at him.

"Well, last year we were working a case - but we went and had dinner after, if you recall, because the case was finished by the afternoon. We went to your flat in the evening. Your niece came round and I let her win at chess."

"She beat you."

"The year before that, I hadn't paid my rent and was sleeping on your couch. You bought me the violin."

"Oh, I remember."

"The year before that, I was ill. You came here. You brought some frankly terrible homemade soup and It's a Wonderful Life and I slept through the whole thing. And the year before, we had only known each other a month and I said I didn't do Christmas, and you said - "

"Bollocks. I said, 'Bollocks, everyone does Christmas, or something like it'."

"Right."

"And this year?"

Sherlock shrugged. "This year we put up a tree in my flat, and I harrassed you endlessly for it."