“‘Third-floor,’” he read out, “‘Mr. Thomas Barlow, Commission Agent.’  Hum!  I think we will look in on Mr. Barlow.”

He stepped quickly up the stone stairs, and I followed, until we arrived, somewhat out of breath, on the third-floor.  Outside the Commission Agent’s door he paused for a moment, and we both listened curiously to an irregular sound of shuffling feet from within.  Then he softly opened the door and looked into the room.  After remaining thus for nearly a minute, he looked round at me with a broad smile, and noiselessly set the door wide open.  Inside, a lanky youth of fourteen was practising, with no mean skill, the manipulation of an appliance known by the appropriate name of diabolo; and so absorbed was he in his occupation that we entered and shut the door without being observed.  At length the shuttle missed the string and flew into a large waste-paper basket; the boy turned and confronted us, and was instantly covered with confusion.

“Allow me,” said Thorndyke, rooting rather unnecessarily in the waste-paper basket, and handing the toy to its owner.  “I need not ask if Mr. Barlow is in,” he added, “nor if he is likely to return shortly.”

“He won’t be back to-day,” said the boy, perspiring with embarrassment; “he left before I came.  I was rather late.”

“I see,” said Thorndyke.  “The early bird catches the worm, but the late bird catches the diabolo.  How did you know he would not be back?”

“He left a note.  Here it is.”

He exhibited the document, which was neatly written in red ink.  Thorndyke examined it attentively, and then asked: 

“Did you break the inkstand yesterday?”

The boy stared at him in amazement.  “Yes, I did,” he answered.  “How did you know?”

“I didn’t, or I should not have asked.  But I see that he has used his stylo to write this note.”

The boy regarded Thorndyke distrustfully, as he continued: 

“I really called to see if your Mr. Barlow was a gentleman whom I used to know; but I expect you can tell me.  My friend was tall and thin, dark, and clean-shaved.”

“This ain’t him, then,” said the boy.  “He’s thin, but he ain’t tall or dark.  He’s got a sandy beard, and he wears spectacles and a wig.  I know a wig when I see one,” he added cunningly, “’cause my father wears one.  He puts it on a peg to comb it, and he swears at me when I larf.”

“My friend had injured his left hand,” pursued Thorndyke.

“I dunno about that,” said the youth.  “Mr. Barlow nearly always wears gloves; he always wears one on his left hand, anyhow.”

“Ah well!  I’ll just write him a note on the chance, if you will give me a piece of notepaper.  Have you any ink?”

“There’s some in the bottle.  I’ll dip the pen in for you.”

He produced, from the cupboard, an opened packet of cheap notepaper and a packet of similar envelopes, and, having dipped the pen to the bottom of the ink-bottle, handed it to Thorndyke, who sat down and hastily scribbled a short note.  He had folded the paper, and was about to address the envelope, when he appeared suddenly to alter his mind.