strolled off towards Henry Street, while Thorndyke and I resumed our journey southward.
"Why were you so secret about that projectile?" I asked my friend as we walked up the street.
"Partly to avoid discussion with the caretaker," he replied; "but principally because I thought it likely that a constable would pass the house and, seeing the light, come in to make inquiries."
"And then?"
"Then I should have had to hand over the object to him."
"And why not? Is the object a specially interesting one?"
"It is highly interesting to me at the present moment," replied Thorndyke, with a chuckle, "because I have not examined it. I have a theory as to its nature, which theory I should like to test before taking the police into my confidence."
"Are you going to take me into your confidence?" I asked.
"When we get home, if you are not too sleepy," he replied.
On our arrival at his chambers, Thorndyke desired me to light up and clear one end of the table while he went up to the workshop to fetch some tools. I turned back the table cover, and, having adjusted the gas so as to light this part of the table, waited in some impatience for my colleague's return. In a few minutes he re-entered bearing a small vice, a metal saw and a wide-mouthed bottle.
"What have you got in that bottle?" I asked, perceiving a metal object inside it.
"That is the projectile, which I have thought fit to rinse in distilled water, for reasons that will presently appear."
He agitated the bottle gently for a minute or so, and then, with a pair of dissecting forceps, lifted out the object and held it above the surface of the water to drain, after which he laid it carefully on a piece of blotting-paper.
I stooped over the projectile and examined it with great curiosity, while Thorndyke stood by regarding me with almost equal interest.
"Well," he said, after watching me in silence for some time, "what do you see?"
"I see a small brass cylinder," I answered, "about two inches long and rather thicker than an ordinary lead pencil. One end is conical, and there is a small hole at the apex which seems to contain a steel point; the other end is flat, but has in the centre a small square projection such as might fit a watch-key. I notice also a small hole in the side of the cylinder close to the flat end. The thing looks like a miniature shell, and appears to be hollow."
"It is hollow," said Thorndyke. "You must have observed that, when I held it up to drain, the water trickled out through the hole at the pointed end."
"Yes, I noticed that."
"Now take it up and shake it."
I did so and felt some heavy object rattle inside it.
"There is some loose body inside it," I said, "which fits it pretty closely, as it moves only in the long diameter."
"Quite so; your description is excellent. And now, what is the nature of this projectile?"
"I should say it is a miniature shell or explosive bullet."
"Wrong!" said Thorndyke. "A very natural inference, but a wrong one."
"Then what is the thing?" I demanded, my curiosity still further aroused.
"I will show you," he replied. "It is something much more subtle than an explosive bullet—which would really be a rather crude appliance—admirably thought out and thoroughly well executed. We have to deal with a most ingenious and capable man."
I was fain to laugh at his enthusiastic appreciation of the methods of his would-be assassin, and the humour of the situation then appeared to dawn on him, for he said, with an apologetic smile—
"I am not expressing approval, you must understand, but merely professional admiration. It is this class of criminal that creates the necessity for my services. He is my patron, so to speak; my ultimate employer. For the common crook can be dealt with quite efficiently by the common policeman!"
While he was speaking he had been fitting the little cylinder between two pads of tissue-paper in the vice, which he now screwed up tight. Then, with the fine metal saw, he began to cut the projectile, lengthwise, into two slightly unequal parts. This operation took some time, especially since he was careful not to cut the loose body inside, but at length the section was completed and the interior of the cylinder exposed, when he released it from the vice and held it up before me with an expression of triumph.
"Now, what do you make it?" he demanded.
I took the object in my fingers and looked at it closely, but was at first more puzzled than before. The loose body I now saw to be a cylinder of lead about half an inch long, accurately fitting the inside of the cylinder but capable of slipping freely backwards and forwards. The steel point which I had noticed in the hole at the apex of the conical end, was now seen to be the pointed termination of a slender steel rod which projected fully an inch into the cavity of the cylinder, and the conical end itself was a solid mass of lead.
"Well?" queried Thorndyke, seeing that I was still silent.
"You tell me it is not an explosive bullet," I replied, "otherwise I should have been confirmed in that opinion. I should have said that the percussion cap was carried by this lead plunger and struck on the end of that steel rod when the flight of the bullet was suddenly arrested."
"Very good indeed," said Thorndyke. "You are right so far that this is, in fact, the mechanism of a percussion shell.
"But look at this. You see this little rod was driven inside the bullet when the latter struck the wall. Let us replace it in its original position."
He laid the end of a small flat file against the end of the rod and pressed it firmly, when the rod slid through the hole until it projected an inch beyond the apex of the cone. Then he handed the projectile back to me.
A single glance at the point of the steel rod made the whole thing clear, and I gave a whistle of consternation; for the "rod" was a fine tube with a sharply pointed end.
"The infernal scoundrel!" I exclaimed; "it is a hypodermic needle."
"Yes. A veterinary hypodermic, of extra large bore. Now you see the subtlety and ingenuity of the whole thing. If he had had a reasonable chance he would certainly have succeeded."
"You speak quite regretfully," I said, laughing again at the oddity of his attitude towards the assassin.
"Not at all," he replied. "I have the character of a single-handed player, but even the most self-reliant man can hardly make a post-mortem on himself. I am merely appreciating an admirable piece of mechanical design most efficiently carried out. Observe the completeness of the thing, and the way in which all the necessities of the case are foreseen and met. This projectile was discharged from a powerful air-gun—the walking-stick form—provided with a force-pump and key. The barrel of that gun was rifled."
"How do you know that?" I asked.
"Well, to begin with, it would be useless to fit a needle to the projectile unless the latter was made
