Exchanging a meaningful look with Holmes, I approached our visitor and knelt down beside him.

“How long have you had this cough?” I said.

He shrugged. “Three weeks, maybe four.”

Looking at his jacket I saw that it hung rather loosely about his torso. “And you’ve lost weight?”

He nodded.

“Night fevers? Sweats?”

Again he nodded, then looking into my eyes, I saw he knew as well as I did what the trouble was.

Returning to my seat, I allowed myself a moment before confirming my diagnosis. “Consumption, I’m afraid.”

Holmes waved the white card. “You think a spell on this island might help?”

“Of course, if it happened to be in the Caribbean, but the Devon coast is too cold at this time of year.” I cast a sidelong glance at Doctor Armstrong. “It might finish him off.”

“That’s it, then,” said Holmes, leaping to his feet. Crossing the room, he pulled the doctor from his chair and patted him heartily on the back. “Off to Barbados with you, my man. My colleague and I shall deal with this other matter.”

The visitor muttered his thanks and left.

“This other matter?” I said, when Holmes had seated himself again.

My friend took a few moments to fill his pipe and light it, puffing away until a cloud of blue smoke had almost engulfed him. “This doctor has been invited to an island, all-expenses paid, for reasons neither he nor we can guess, except for the ‘wonderful opportunity’ mentioned in the invitation. The doctor does not know his benefactor and has no conception of what may occur on his arrival. Following my initial interview with Armstrong and my investigations yesterday, I took the liberty of amending the doctor’s tickets to include another passenger – your wife.”

“You wish me to go in his place? And with Mary?” I sat back, aghast.

“To the Eastern Isles, yes.” Holmes dropped his voice. “My enquiries have unearthed a few odd, but important facts – as well as the good doctor, seven other individuals have been invited to this island. I suspect each of them has no idea as to why, which is suggestive, don’t you think?”

“Of what, Holmes?”

“Of murder, Watson. This has all the hallmarks of a master plan – something that has put the perpetrator to a great deal of trouble.”

A short burst of laughter escaped my lips before I could stop it. “Sorry, Holmes, but this whole thing sounds completely ridiculous.”

Holmes nodded. “Indeed it does, and I should think so to if it were not for one small fact.” Standing, he reached behind his chair to the bookshelf and took down a single volume, sheathed in a colourful paper dust-jacket with white and red lettering. “Here,” he said, waving the item. “A piece of fiction by the female authoress we know as Mrs Christie – I believe your wife has read a few of her efforts.”

I took the proffered volume and looked at the cover. “They changed the title?”

Holmes grunted. “Ah yes, some issue with offending certain communities, I believe. However, the point is that this story starts off with eight individuals being invited to a mysterious island where they are picked off, one by one, until there are none.”

I considered this for a moment, then said, “And you want Mary and I to go there and find out if this is some copycat killer?”

“Precisely.”

“And you don’t think this mysterious person may cotton on to the fact that I am not Doctor Armstrong?”

Holmes shook his head. “I suspect Armstrong has never actually met his intended benefactor and the latter’s knowledge of him likely relates to personal details, education and so forth. Also, as it happens, you do bear a vague resemblance to Armstrong in terms of height, bearing etcetera, though I suggest the application of a little hair dye and the removal of your moustache will aid the charade.”

“Shave off my moustache?” I exclaimed, fingering my facial development. “But I grew it especially for Mary – she likes the way it tickles her–”

“Yes, yes, spare me the details, Watson. The point is, the only fly in the ointment from the point of view of our would-be murderer, will be the appearance of Mary. And I’m certain you’ll be able to explain that away without arousing his suspicions.”

“But surely,” I protested, “It would be easier to simply prevent each of these people from going to the island in the first place?”

“Of course it would, Watson, but then we should not find out who the murderer is.”

I let out a long sigh, though I could not conceal my curiosity. “Seems a bit of a risk.”

“Yes, which is why I shall be coming along too, though no-one must know of my presence in order that I may have time to evaluate the situation and catch the killer before he, or she, strikes.” He raised an eyebrow. “Is the game afoot?”

I smiled. “Yes, Holmes, the game’s afoot.”