door behind him and put the key into his pocket. He led me through a small gate, down a cluttered alley, then quickly through two narrow passageways and into a courtyard behind the slaughterhouses. The key and the apron he discarded there. I saw he had a cab waiting, the horse tethered to an unlit lamppost. There was no cabman in sight. "Take me home, Watson," he said. "You should not have come. But, since you are nevertheless here, I confess myself glad of the chance to unburden myself of the awful things that I have seen and done. Take me home, and I shall conceal nothing from you."
I drove and Holmes sat in back, meditating or sleeping, I could not tell which. We passed three constables, but I did not stop. He bade me halt at a certain mews not far from Baker Street. "The cabman will be here in half an hour," he said, as he tended expertly to the horse. "He has been paid in advance, and we need not wait."
"I believe you must think me most utterly mad, Watson," said Holmes, after he had exchanged his rough clothes for a dressing-gown, meticulously cleansed himself of dirt and spattered blood, fetched the Persian slipper in which he kept his tobacco, and settled back in his chair. "You have not loosened your grip on that service revolver of yours for the last hour. Your fingers must be cramped by now, you have been clutching it so strongly—Ah," he said, as I opened my mouth to deny this, "no use in your protesting your innocence. Your hand has not strayed from the pocket of your robe for an instant, and the distinctive weight of your pistol is quite clearly evident in it. I may be mad, my dear Watson," he said with a smile, "but I am not blind."
This was the Holmes I knew, and I relaxed. I knew I had nothing to fear from him.
His hand hesitated over his rack of pipes, selected his clay-stemmed pipe, and filled it with shag. "Indeed, Watson, at times during these last months I would not have disputed it with you myself. It would have been a relief to know myself mad, and that all I have seen and conjectured to be merely the delusions of a maniac."
He teased a coal out of the grate and lit his pipe with it. "To begin, then, with the missing corpse." He puffed the pipe until its glow matched that of the fire behind him. "Or, perhaps better," he said, "I should begin with the London cannonade." He raised a finger at my imminent objection. "I have promised to tell all, Watson, and I shall. Pray let me go about it in my own way.
"My brother Mycroft," he continued, "made a most interesting comment when I discussed the matter of the cannonade with him. He mentioned that when a highly powered cannon is fired, an observer at the front lines ahead of the artillery and distant from the firing will hear a very distinct report at the instant the shell passes. This is the crack of displaced air. This report comes considerably in advance of the actual sound of the cannon firing. If our ears were but sensitive enough to hear it, he informed me, this report would be heard as two distinct waves, one of the air compressed by the shell, and another of the air rushing inward to fill the vacuum left behind it. An aeroship which traversed faster than the velocity of sound would produce a like crack, and, if it were large enough, the two waves would be heard as distinct reports.
"My brother discussed this only as an abstract but interesting fact, but I know him well enough to understand the meaning behind his words.
"Taking this as a provisional theory, then, and judging by the fact that observers noted the timing between the two reports was briefer in the north than in the south of London, we find that the hypothetical aeroship must have been slowing down as it traveled south."
"But Holmes," I said, my mind in total consternation, "an aeroship? And one which moves faster than an artillery shell? No nation on God's Earth could make such a thing, not to mention the impossibility of keeping it secret."
"Precisely," said Holmes. He took another puff from his pipe. "This brings us to the case of the missing corpse. I had been looking for a reason to investigate south of London, and