My very good friend Mr. Sherlock Holmes was prone to the occasional and sporadic bout of melancholy, as I believe I have had cause to mention once or twice in my recording of his cases and personal history. During most episodes such as these he would cast all six feet of his length onto our sofa and smoke a copious wealth of shag tobacco and speak little, if at all.

On other, more infrequent occasions, he would vanish from our rooms for days on end, at last returning in milder humour but still with no fuller explanation as to where it was exactly that he went.

The last of these outings, to my memory, happened upon the fourteenth of September of some year, perhaps the other.

The sitting-room door flung open wide, and Holmes stood upon its threshold.

"Watson!" said he, all vim and vigour returned. "It is me!"

My yellow-backed novel had fallen to my lap with the surprise of him.

"So it is!" I agreed. "Welcome home, er, Holmes. How are you feeling, my dear fellow?"

He waved my concern to one side and strode across to the mantel, and from there to his chair.

"I am all tickety-boo now," he said. "I had a bit of a thing, and a whatnot, and – pfffft! – well, you know."

I frowned.

"When did you have the thing and the whatnot?" I enquired. "And what exactly might they be?"

My friend performed a vague mime in the air.

"That," he explained helpfully. "What time is dinner?"

"Never mind about dinner," I said sternly. "What is 'that', and what was this?"

I repeated the mime for the sake of comprehension. It involved several twirls of an index finger and a repeated stabbing motion.

Holmes coloured slightly.

"It looks rather vulgar when you do it, Watson," said he with a flinch. "I am not sure what to say."

"I do hope it was nothing illegal, Holmes."

He shook his head violently, looking somewhat appalled.

"Well, if you do not wish to tell me, then I shall not persist in pressing you," I said. "You look far better now at any rate. Dinner is at seven."

We sat in companionable silence and smoked our pipes for several minutes. I slowly became aware of an irregularity in Holmes's demeanour. His right arm appeared to bother him, for he rubbed at it at intervals and winced around his pipe stem. I did my best to disregard it until the second I could not.

"What is the matter with your arm, Holmes?"

He clenched down hard on the soft amber, then, scowling, turned his gaze to mine.

"Watson, you made me jump," he complained. "I almost chomped my pipe in half."

"Your arm," I repeated slowly. "What is the matter?"

My friend stared at his left arm as if it were improperly attached to all the rest of him.

"The other one?" I prompted.

"There is nothing whatsoever the matter with my right arm," said Sherlock Holmes.

"I don't believe you. Show it to me."

He waved it at me in irritation.

"No," I said, "what I mean is, please remove your jacket and roll up your shirt-sleeve."

Holmes looked at me in horror.

"It is too early in the afternoon for an arm-wrestle, Watson," said he.

"For goodness sake," I replied, "I don't wish to arm-wrestle you; I want to look at your arm. It is causing you discomfort."

"No it isn't."

"I really think that it is."

"It truly is not."

We glared at each other, exhausted.

"If you rub at your arm just once more," I said warningly, "then I shall wrestle you. I shall wrestle you to the rug and I shall inspect your arm quite forcibly."

My friend appeared to shiver at the thought of this.

At the very least, he ceased his fitful jitter and by and by our conversation turned to the gossip of the day and comment on the freshest casework. Our roast beef dinner was enjoyed, and later, after the apple tart and port, we read together by the barren hearth as the evening shadows spread. My glance often stretched across to Holmes, for it being the first day back from the great wherever, I still retained some small concern for his well-being. Content enough, he seemed to me, engrossed as he was in a serious leather-bound. (The previous time, it was The Adventures of Pinocchio – which always has a strange effect on Holmes and forecasts further trouble.)

Trouble enough, however, when deep within his study and as an involuntary movement, his left hand moved to agitate his upper right arm, and there again the painful wince. He froze almost immediately, but, alas, it was too late.

I swooped upon him.

"Off!" I said. "Off with your jacket."

He batted at me feebly.

"Watson," said he, "I cannot allow you to undress me."

"I am your doctor," I replied. "You ridiculous man."

I swept his jacket to one side and battled with the silver link. It proved reluctant to relinquish the strong grip upon his cuff. I managed it at last and began to tug at the material.

"You had jolly well better not rip it," said Holmes, laying back as if in a near faint. "It is a Henry Jaques, and it cost me eighteen shillings."

"You have rather more money than sense," I informed him.

I rolled up the shirt-sleeve as far as it went. A small white pad tied around with a linen strip met my eye.

"Holmes," I said, soft, "what on earth have you done? And, what is more important – are you still doing it?"

He wrestled free.

"It is not what you think!" he squeaked shrilly, indignant. He hesitated then. "What is it that you think?"

"That you are injecting a narcotic. That you are an addict, Holmes."

"No!" He pulled his arm clear of my grip.

"Then what is the pad for, and why on earth the secrecy?"

"Watson, I implore you!"

"Please explain it to me, Holmes."

His lips curled back, his teeth exposed. If he had been a terrier then I should have feared that he might bite me, such was his conflict.

"Watson, you are an absolute nuisance," said he. "You do not allow me a shred of my privacy."

He picked at the linen, unwrapped it and at last plucked it free.

"There," he said, frowning, displaying his arm. "Make of that what you will."

I stared at the flesh, red-sore and black lined.

"It is a tattoo," I said slowly.

"Your powers of deduction are awe-inspiring."

I leaned in closer, placed a finger to the pucker not yet an inch in its circumference.

"It is a tattoo of a..." and here I stopped.

I looked at Holmes. He glared.

"Of a moustache," I finished, dully.

If looks could kill, then I should be a dead man.

"Holmes," I said at last, after an interminable interval, "why do you have a tattoo of a moustache upon your arm?"

"It seemed like a good idea at the time," said he – as if that should explain all and everything.

"Yes – and you said that about the teapot too, remember," I reminded him. "And we both know what became of that." I shook my head. "I don't understand."

"No," said Holmes. "I don't suppose you would. I have an old friend at the docks who-"

"Yes, you do have some odd friends," I interrupted, beginning to smile through the shock. "Holmes, I am more relieved than I can possibly admit that you have not returned to your morocco case. But I am sure that you don't need me to tell you how incongruous a tattoo is for a man of your distinction. You will regret it in the years to come, do mark my words."

Holmes rolled down his shirt-sleeve, and he fastened up his cuff.

"Perhaps I shall," he murmured. "But then again, perhaps, I won't."

And we spoke of it no more, but every now and then I catch a glimpse of it, through a thin sleeve or an awry dressing-gown, and still I wonder.