Our neighbor turned again, looked doubtfully at his plate and the table-cloth about it, and then shot a keen glance in the direction of Hewitt.  He said nothing, however, but took his coffee and his bill, deliberately drank the former, gazing quietly at Hewitt as he did it, paid the latter, and left.

Immediately Hewitt was on his feet and, taking an umbrella, which stood near, followed.  Just as he reached the door he met our late neighbor, who had turned suddenly back.

“Your umbrella, I think?” Hewitt asked, offering it.

“Yes, thanks.”  But the man’s eye had more than its former hardness, and his jaw muscles tightened as I looked.  He turned and went.  Hewitt came back to me.  “Pay the bill,” he said, “and go back to your rooms; I will come on later.  I must follow this man—­it’s the Foggatt case.”  As he went out I heard a cab rattle away, and immediately after it another.

I paid the bill and went home.  It was ten o’clock before Hewitt turned up, calling in at his office below on his way up to me.

“Mr. Sidney Mason,” he said, “is the gentleman the police will be wanting to-morrow, I expect, for the Foggatt murder.  He is as smart a man as I remember ever meeting, and has done me rather neatly twice this evening.”

“You mean the man we sat opposite at Luzatti’s, of course?”

“Yes, I got his name, of course, from the reverse of that gold medal he was good enough to show me.  But I fear he has bilked me over the address.  He suspected me, that was plain, and left his umbrella by way of experiment to see if I were watching him sharply enough to notice the circumstance, and to avail myself of it to follow him.  I was hasty and fell into the trap.  He cabbed it away from Luzatti’s, and I cabbed it after him.  He has led me a pretty dance up and down London to-night, and two cabbies have made quite a stroke of business out of us.  In the end he entered a house of which, of course, I have taken the address, but I expect he doesn’t live there.  He is too smart a man to lead me to his den; but the police can certainly find something of him at the house he went in at—­and, I expect, left by the back way.  By the way, you never guessed that simple little puzzle as to how I found that this was a murder, did you?  You see it now, of course?”

“Something to do with that apple you stole, I suppose?”

“Something to do with it?  I should think so, you worthy innocent.  Just ring your bell; we’ll borrow Mrs. Clayton’s sewing-machine oil again.  On the night we broke into Foggatt’s room you saw the nutshells and the bitten remains of an apple on the sideboard, and you remembered it; and yet you couldn’t see that in that piece of apple possibly lay an important piece of evidence.  Of course I never expected you to have arrived at any conclusion, as I had, because I had ten minutes in which to examine that apple, and to do what I did with it.  But, at least, you should have seen the possibility of evidence in it.