"Somethin' wrong, Doc?" I started guiltily at Billy's sleepy voice behind me, hastily palming the diamond and slipping it into my jacket pocket.

"No, lad, it's all right. Go back to sleep, I'll smoke out the bathroom window." A little cold water seemed an excellent idea in any case; I could still hardly believe I wasn't dreaming, despite the sobering weight in my pocket.

Safely locked in the bathroom, I gingerly drew out the stone again and examined it closely under the gaslight. I must have been mistaken, surely! This couldn't be the real Koh-i-Noor, it had to be a fake, no matter how dazzling it was, or how closely it matched the real diamond's weight, size and shape... but thanks to Holmes, I knew other tests for just this occasion. I breathed on the stone; fog formed for a moment, then vanished again just as quickly. All right, first test passed... I opened my spare notebook to a filled page, put the stone onto it flat side down and tried to read the words through it – not a single letter could be clearly seen. Damn! One more... I poured some water from the washstand jug into the basin and dropped in the stone: it sank straight to the bottom, followed closely by my stomach.

Dear God... I sat unsteadily on the edge of the bathtub, mind reeling. As far as I could tell in this makeshift laboratory, that stone glinting wickedly up at me from the depths of the basin was the genuine article. There was certainly no mistaking it for any other diamond, not after the papers had reported its recutting only five years earlier, photographs and all! Although much improved in appearance, the stone had no longer fitted its original armlet, and been reset into two pieces for her Majesty, a brooch and a circlet. And wouldn't that be the perfect diamond for a master thief like Sylvius to steal and replace with a fake: one that was meant to detach so easily from its setting! The replica stone wouldn't even need to be a perfect match – just good enough, as Mycroft would say, to deceive the average civilian... Taylor had finally mastered his craft, it seemed, and Ikey Sanders was most likely the latest accessory to Sylvius's crime.

I jumped at a tap on the door. "Darling? Billy said you looked awfully pale just now, are you all right?"

"I'm fine, dear, honestly! I'd love another cup of tea, though!" I plucked the diamond out of the water and dried it, cursing my fevered imagination that made the cool carbon lump feel like a hot coal. Never mind deductions, what the devil was I going to do with the infernal thing now? It couldn't stay in the flat with the others here, God only knew when Sylvius had smuggled the stone in, or when he and his thugs would be back for it! I could almost admire the sheer audacity of the man: hiding stolen goods in the one place in London no one would ever think to look... Now, there was a thought...

~0~

"Visitors?" Mrs. Hudson looked oddly embarrassed. "Well, yes, I've had a fair few in since the funeral! I'm sorry, Doctor," she added, patting my shoulder. "But you know how it is when it's somebody famous, and I didn't see any harm in letting people pay their respects."

"Lettin' 'em 'ave a good snoop, don't you mean?" Billy snorted.

"We can't all afford to let good rooms gather dust, dear!" the woman replied tartly. "Every penny helps."

"There's an entry fee?" I must have been too distracted to notice a collection box on the way up. "Well, well, never mind that now. I don't suppose you remember anyone in the last fortnight or so who stood out? A smooth, foreign-looking gentleman, dark hair, olive skin?" I could only assume that Sylvius might more closely resemble his father.

"I don't think so... No, I'm sorry, Doctor, I don't remember anyone like that."

"All right, what about..."

"You wouldn't be describing this Count Sylvius, would you, John?" Mary interrupted sharply. "Why should he come here, of all places?"

Billy snickered at my cornered expression. "The missus 'as you there, Doc! You thinkin' Sylvius might want a nosey at Mr. 'Olmes's papers, too, see wot the guv'nor 'ad on 'im?"

I almost sagged in relief. "Exactly, lad, well done! Mrs. Hudson, have you ever left your visitors alone up here? No, of course not, silly of me." Even a well-intentioned tripper mightn't be able to resist pocketing a souvenir.

"And the 'S' file still has Sylvius's name in it," Mary added, "so if anyone did come for that, they've left empty-handed."

"So far," I agreed, sighing deeply. "And that's what worries me. I hate to say it, you three, God knows I do... but I think... it's time to involve the Yard. These files have been sitting here unprotected for far too long, and Sylvius or his thugs could be back at any time to set fire to the lot."

"Just like last time," Mary murmured in concern, slipping her hand back into mine. "What do you need us to do?"

I squeezed her hand with a grateful smile. "You three need to get the file on Sylvius to Scotland Yard, and tell Lestrade what's going on. Mrs. Hudson, lock up the house and take the keys with you. We're doing this one by the book, and I don't want there to be any doubt about how Sylvius got in – assuming he comes tonight, of course."

"John–!"

"You needn't worry about me, love," I added hastily, sternly suppressing any twinges of guilt at the look on my wife's face. "I'll be safe outside, watching the back door. If Sylvius breaks in, I can keep him upstairs from the ground floor until the police arrive. I brought the Webley, remember?"

"And if he breaks in at the front door?" Mrs. Hudson frowned.

"He wouldn't dare," Billy scoffed. "S'no area out front, and the fog ain't thick enough!"

"Quite right," I nodded, ignoring for the moment the fact that Billy had obviously given thought to the problem in the past. "His best chance is the back door. I'll be fine, Mary," I repeated firmly. "Sylvius likely won't come tonight, anyhow. And if he does, he'll be the one caught off guard, not me. I shan't do anything foolish, I promise."

"But you can't promise that!" Mary burst out, eyes glistening angrily. "You never can!"

I shook my head, heart aching at the anguish in her voice. I, too, had felt so sure that my wife would never have to spend another sleepless night... "I'm sorry, Mary, I truly am... but someone has to stay, and it can't be any of you!" I drew Mary close and held her, stiff and trembling. "Remember: Sylvius doesn't know yet what evidence Holmes collected, or how many people have seen it. He's a careful man, he won't implicate himself in a crime unless he sees no other way, and I will take the greatest care not to force his hand. It's the only way, Mary, believe me," I coaxed. "The sooner you three get to the Yard, the sooner I... the sooner we can put him away for good."

Mary sighed deeply and rested her head on my shoulder. "All right..." She looked up again, biting her lip. "But John... I'm so sorry, but this has to be the last time you do something like this. No more police work. I want my husband home from Switzerland."