A paraffin lamp was on the floor in a recess of the hall, and this our conductor took up when he had elosed the street door.

"This is the room," he said, turning the key and thrusting the door open; "the library they call it, but it's the front parlour in plain English." He entered and, holding the lamp above his head, stared balefully at the broken window.

Thornd.y.k.e glanced quickly along the floor in the direction that the missile would have taken, and then said-

"Do you see any mark on the wall there?"

As he spoke, he indicated the wall opposite the window, which obviously could not have been struck by a projectile entering with such extreme obliquity; and I was about to point out this fact when I fortunately remembered the great virtue of silence.

Our friend approached the wall, still holding up the lamp, and scrutinised the surface with close attention; and while he was thus engaged, I observed Thornd.y.k.e stoop quickly and pick up something, which he deposited carefully, and without remark, in his waistcoat pocket.

"I don't see no bruise anywhere," said the caretaker, sweeping his hand over the wall.

"Perhaps the thing struck this wall," suggested Thornd.y.k.e, pointing to the one that was actually in the line of fire. "Yes, of course," he added, "it would be this one-the shot came from Henry Street."

The caretaker crossed the room and threw the light of his lamp on the wall thus indicated.

"Ah! here we are!" he exclaimed, with gloomy satisfaction, pointing to a small dent in which the wall-paper was turned back and the plaster exposed; "looks almost like a bullet mark, but you say you didn't hear no report."

"No," said Thornd.y.k.e, "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 a.s.sisted; and I could not suppress a faint smile as I noted the earnestness with which Thornd.y.k.e 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 bas.e.m.e.nt.

"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 Thornd.y.k.e, 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 pa.s.sing when it happened, sir, I hear."

"Yes," answered Thornd.y.k.e; 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 ill.u.s.trated 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 Thornd.y.k.e 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 princ.i.p.ally because I thought it likely that a constable would pa.s.s 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 Thornd.y.k.e, 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, Thornd.y.k.e 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 Thornd.y.k.e 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 bra.s.s 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 sh.e.l.l, and appears to be hollow."

"It is hollow," said Thornd.y.k.e. "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 sh.e.l.l or explosive bullet."

"Wrong!" said Thornd.y.k.e. "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."