We had once more turned into John Street and now perceived a man, standing on the wide doorstep of the house with the shattered window, looking anxiously up and down the street.

“Do either of you gents know anything about this here?” he asked, pointing to the broken pane.

“Yes,” said Thorndyke, “we happened to be passing when it was done; in fact,” he added, “I rather suspect that the missile, whatever it was, was intended for our benefit.”

“Oh!” said the man.  “Who done it?”

“That I can’t say,” replied Thorndyke.  “Whoever he was, he made off on a bicycle and we were unable to catch him.”

“Oh!” said the man once more, regarding us with growing suspicion.  “On a bicycle, hay!  Dam funny, ain’t it?  What did he do it with?”

“That is what I should like to find out,” said Thorndyke.  “I see this house is empty.”

“Yes, it’s empty—­leastways it’s to let.  I’m the caretaker.  But what’s that got to do with it?”

“Merely this,” answered Thorndyke, “that the object—­stone, bullet or whatever it may have been—­was aimed, I believe, at me, and I should like to ascertain its nature.  Would you do me the favour of permitting me to look for it?”

The caretaker was evidently inclined to refuse this request, for he glanced suspiciously from my companion to me once or twice before replying, but, at length, he turned towards the open door and gruffly invited us to enter.

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.

Thorndyke 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 Thorndyke 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 Thorndyke, 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.