“I’ve been at his very elbow all the morning. You’ve seen me as an old lady, Watson. I was never more convincing. He actually picked up my parasol for me once. ‘By your leave, madame,’ said he - half-Italian, you know, and with the Southern graces of manner when in the mood, but a devil incarnate in the other mood. Life is full of whimsical happenings, Watson.”

“It might have been tragedy.”

“Well, perhaps it might. I followed him to old Straubenzee’s workshop in the Minories. Straubenzee made the air-gun - a very pretty bit of work, as I understand, and I rather fancy it is in the opposite window at the present moment. Have you seen the dummy? Of course, Billy showed it to you. Well, it may get a bullet through its beautiful head at any moment. Ah, Billy, what is it?”

The boy had reappeared in the room with a card upon a tray. Holmes glanced at it with raised eyebrows and an amused smile.

“The man himself. I had hardly expected this. Grasp the nettle, Watson! A man of nerve. Possibly you have heard of his reputation as a shooter of big game. It would indeed be a triumphant ending to his excellent sporting record if he added me to his bag. This is a proof that he feels my toe very close behind his heel.”

“Send for the police.”

“I probably shall. But not just yet. Would you glance carefully out of the window, Watson, and see if anyone is hanging about in the street?”

Watson looked warily round the edge of the curtain.

“Yes, there is one rough fellow near the door.”

“That will be Sam Merton - the faithful but rather fatuous Sam. Where is this gentleman, Billy?”

“In the waiting-room, sir.”

“Show him up when I ring.”

“Yes, sir.”

“If I am not in the room, show him in all the same.”

“Yes, sir.”

Watson waited until the door was closed, and then he turned earnestly to his companion.

“Look here, Holmes, this is simply impossible. This is a desperate man, who sticks at nothing. He may have come to murder you.”

“I should not be surprised.”

“I insist upon staying with you.”

“You would be horribly in the way.”

“In his way?”

“No, my dear fellow - in my way.”

“Well, I can’t possibly leave you.”

“Yes, you can, Watson. And you will, for you have never failed to play the game. I am sure you will play it to the end. This man has come for his own purpose, but he may stay for mine.” Holmes took out his notebook and scribbled a few lines. “Take a cab to Scotland Yard and give this to Youghal of the C. I. D. Come back with the police. The fellow’s arrest will follow.”

“I’ll do that with joy.”

“Before you return I may have just time enough to find out where the stone is.” He touched the bell. “I think we will go out through the bedroom. This second exit is exceedingly useful. I rather want to see my shark without his seeing me, and I have, as you will remember, my own way of doing it.”