After the fact, Watson was never exactly sure how he had come to this conclusion.

It started normally enough – or as normal as things got when Holmes was so involved in a case. He rose from his silent contemplation and suddenly declared, "We shall have to dance, Watson."

Watson knew better than to argue, though there was some contest as to who would lead, as they were only a few inches from the same height, but Holmes settled that by stating that Watson's limp would impede him in leading, especially in such confined quarters. He almost certainly caught the brief flash of irritation on the doctor's face before it was quashed, but said nothing of it.

Watson stood slowly as Holmes crossed the room to wind the gramophone – a gift in payment from a client of Holmes' – and then returned to the centre of the room, gesturing for Watson to join him. The doctor suppressed a sigh, but acquiesced, placing a hand on his companion's shoulder and holding the other out in a rather petulant, childlike fashion. He could see Holmes' smirk flickering at the edge of his mouth as he took Watson's hand in his own, setting the other on the doctor's waist as the waltz started up.

They began to dance rather clumsily at first, before the slight and brief fight for dominance ended with Watson's realisation that this battle was lost before had ever begun. After that, the dance proceeded fairly smoothly, even with Watson's limp and Holmes' flagrant disregard of anything approaching grace, though the man was usually host to an overabundance of such. Watson was almost certain he was doing it on purpose, and he said as much. Holmes merely quirked a corner of his mouth in that infuriating smirk of his that said he had procured exactly the reaction he had set out to. Nonetheless, he then seemed to at least put some effort in, and they carried on much better than they had begun.

"You know, Holmes," Watson began, trailing off as Holmes' ever-sharp eyes pierced him, then managed to find his voice again, "I don't suppose Mary was truly right for me."

"Of course not. She could not even tell that your injuries are not yet fully healed."

Watson started, halting the dance as Holmes pulled him forwards, putting too much weight on his injured leg and causing him to stumble. Holmes caught him, as he always did, and Watson allowed himself to lean on his friend for a fraction longer than he usually would. Longer than he would in the presence of others, certainly. Before he even had a chance to ask how Holmes had noticed, the man was speaking.

"You are favouring your right side more heavily. Your cane is wearing quickly – You'll have to have that seen to, my friend – and you carry and hold most everything with your right hand when you can."

Watson allowed the ghost of a smile to pass over his features where Holmes could not see, then straightened and brushed off the shoulders of his friend's waistcoat. Before he could turn away, Holmes reached out and tucked a stray strand of hair behind the doctor's ear, then returned to the seat he had been occupying before the dance had begun, as if nothing had occurred. After a moment of silence and contemplation, Watson limped back to his own chair and sat down, picking up his now-cold cup of tea, listening to the gramophone slowly wind down.

"In any case, old boy, Miss Morstan would never have had all of you. Least of all the most important part." Holmes said suddenly, looking directly at Watson in a way that made him uncertain, for reasons he could not fathom. Still, he affected a smile and raised an eyebrow in query.

"And which part would that be?"

"Your heart, of course."

That shocked Watson into silence, and he contemplated Holmes' words, even as the man looked away, and Watson instantly knew that Holmes had given away more of himself than he had intended to. The doctor smiled softly, sipping at his cold tea once before setting the cup down.

"Of course," He echoed, "That belongs here. Has done for a long time now, by my reckoning, Holmes."