"looks almost like a bullet mark, but you say you didn't hear no report."
"No," said Thorndyke, "there was no report; it must have been a catapult."
The caretaker set the lamp down on the floor and proceeded to grope about for the projectile, in which operation we both assisted; and I could not suppress a faint smile as I noted the earnestness with which Thorndyke peered about the floor in search of the missile that was quietly reposing in his waistcoat pocket.
We were deep in our investigations when there was heard an uncompromising double knock at the street door, followed by the loud pealing of a bell in the basement.
"Bobby, I suppose," growled the caretaker. "Here's a blooming fuss about nothing." He caught up the lamp and went out, leaving us in the dark.
"I picked it up, you know," said Thorndyke, when we were alone.
"I saw you," I answered.
"Good; I applaud your discretion," he rejoined. The caretaker's supposition was correct. When he returned, he was accompanied by a burly constable, who saluted us with a cheerful smile and glanced facetiously round the empty room.
"Our boys," said he, nodding towards the broken window; "they're playful lads, that they are. You were passing when it happened, sir, I hear."
"Yes," answered Thorndyke; and he gave the constable a brief account of the occurrence, which the latter listened to, notebook in hand.
"Well," said he when the narrative was concluded, "if those hooligan boys are going to take to catapults they'll make things lively all round."
"You ought to run some of 'em in," said the caretaker.
"Run 'em in!" exclaimed the constable in a tone of disgust; "yes! And then the magistrate will tell 'em to be good boys and give 'em five shillings out of the poor-box to buy illustrated Testaments. I'd Testament them, the worthless varmints!"
He rammed his notebook fiercely into his pocket and stalked out of the room into the street, whither we followed.
"You'll find that bullet or stone when you sweep up the room," he said, as he turned on to his beat; "and you'd better let us have it. Good night, sir."
He 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
