Prompt: Watson's favourite Christmas carol, from sirensbane

I had not thought, upon my marriage, that Mary and I would host many gatherings. Neither of us had any family, and were both of quiet habits that had led us to form few friendships, certainly not enough to make up a party.

By our second year of marriage, however, Mary raised the idea of a Christmas gathering, suggesting that we could invite her former employer as well as several of her schoolmates and our neighbors. I did not wish to refuse such a request, knowing how my wife felt grateful to her employer and her friends for providing her a home and assistance when she had no one else, and now wished to pay them back in some small way. Instead, I thought of my own small circle, and was pleased to find that with several Yarders and some doctors I knew, I was able to add considerably to the gathering.

"Do you think Mr. Holmes will come?" Mary asked anxiously. Invitations had duly been sent, and responses had begun to arrive. "I should hope so; I know you will be glad to see him."

"Holmes detests social gatherings," I said. "Save as an exercise in observation and deduction." I did not expect him to attend, though I hoped he would make an exception to his Bohemian ways. "He will likely not give a response. It will depend on his mood on the day."

Preparations continued, and soon the day itself arrived. Mary, leading our small kitchen staff, had outdone herself in preparing a sumptuous feast, and the company was lively. Despite never having met before, the Yarders and their wives seemed to get along very well with Mary's school friends, and I found myself greatly enjoying the company of the Foresters, Mary's erstwhile employers.

As for Holmes, he had arrived considerably after the party had begun, though I had expected this and did not mind. His arrival caused a minor commotion as everyone realized the famous detective was among them, but after a few casual deductions, done with Holmes's typical flair, and a wink in my direction, he was left alone to smoke his pipe and observe as he pleased.

"Come, we should have some music. It is Christmas!" Mrs. Forester said after the meal, at a lull in the conversation.

"I was hoping someone would ask. It is not a party without music," Mary said. She seated herself at our piano, which while relatively inexpensive and upright rather than a grand, was a piece we were proud to have been able to afford. I knew little of music, aside from what I had learned accompanying Holmes to concerts, but its sound was a fine one to me, and Mary assured me it was as good a quality instrument as we could hope to have. I had often enjoyed hearing her practice during the day. "I have been practicing," she added. "Now that I have someone to play for." She sent me a loving look, and several of her school friends began to giggle.

Everyone settled in to listen and sing along, when Mary cleared her throat and said, "However, I am not the only musician here." I knew at once what she was thinking and tried to surreptitiously stop her, for Holmes never performed in public, and indeed, rarely played for anyone other than himself. I doubted I counted as audience since he so often played at two in the morning.

But Mary continued with a smile. "Mr. Holmes? Would you care to join me?"

To my shock, Holmes took up a spot next to her, his violin ready. I had not even seen him arrive with his instrument and wondered for a moment how he had managed to sneak it past me, before I realized such an exercise was pointless. I could not figure it out if I had all night, but it would be little more than child's play to him. Even more astonishing was that they had obviously planned this. Neither ever played duets that I knew, and I wondered when they had found the time to practice without my noticing.

I soon forgot my shock as they began to play; the familiar chords of Silent Night filling the room, and soon the entire party was engaged in singing along. There are few things as enjoyable as a room full of people enjoying music together, particularly when it is a small, intimate group of friends and family. I am convinced no activity brings us closer together as humans.

Mary and Holmes finished their second piece, God Rest Ye, Merry Gentlemen, to a round of applause. "Don't stop!" One of the Yarders called out, to general laughter. I wondered if anyone in the room realized what a privilege it was to hear Holmes play.

"For our next piece, we will be playing one of John's favorites," Mary said. I looked at her quizzically, not sure which piece she meant. I could hardly remember telling her that I preferred one Christmas carol over another. Though the moment she began to play, I smiled in recognition of the slow, chanting melody of O Come O Come Emmanuel.

It was indeed a favorite of mine, for the chanting reminded me of the ancient origins of the holiday, and always put me in a peaceful mood. I had never seen it played thusly, however. Holmes and Mary's two instruments melded together perfectly, switching off on playing the melody until they came together in harmony during the rousing chorus. I found I was holding my breath, for the effect was so beautiful and showed off the skill of both musicians. I confess that while I had known both of them to be excellent musicians (Holmes particularly so; I believe he could have had a place in any London orchestra had he not turned to solving crime), the piece elevated them both until they astonished me with their skill.

"Bravo! Brava!" I cried when they finished, to rapturous applause from all our guests. Holmes bowed, his normally pale cheeks flushed and Mary curtsied prettily, then bowed in thanks to my friend for accompanying her, a gesture he returned.

"You were wonderful," I said, finding Mary after she had been congratulated by the other attendees.

"Thank you," Mary said. "I have never had the good fortune of playing with so fine a musician before. I am only glad I was able to keep up."

"Mrs. Watson, do not sell yourself short. You have remarkable skill," my friend said. "I have not had much opportunity to play with other musicians at all, and I confess I do not believe most of them could have learned to play so many pieces in duets so quickly."

Mary blushed red, knowing how rare his compliments were. "Thank you, Mr. Holmes."

"Really, you were both magnificent," I said. "I am almost as impressed that you found the time to practice without my knowing."

"Now, Watson, is that really so surprising?" Holmes asked, and I had to laugh.

"No, I suppose not."

"Still, they were not really such difficult pieces," Mary said, as Holmes was drawn into an argument with a Yard officer about a crime from several years previously. "Christmas carols are usually simple enough that anyone may sing or play them with ease. O Come O Come Emmanuel in particular is a chant; I hardly had a left hand section to play at all."

"You sound very much like Holmes right now, did you realize?" I asked, causing Mary to laugh. "You organized a wonderful party, Mary. It was an excellent evening."

"We shall have to make a tradition of it," she answered. "Though I think I will not be able to convince Mr. Holmes to play again."

"I am impressed enough you managed it this time," I said.

A/N: I had written this entire story about Carol of the Bells, then thought to look it up and realized that song wasn't written until 1914 and so Mary couldn't have played it. Do your research first, lesson learned. So I went and changed it all to O Come O Come Emmanuel, which dates back so far I knew I had to be safe.

Victorians loved sitting around the piano having Christmas carol sing-alongs. Most houses that could afford it had a piano, and most governesses would have taught piano, so I figured it's safe to assume Mary did too.