“If you have finished, Doctor, I’ll be off and have a look round Little Italy.  Those four Italians oughtn’t to be difficult to find, and we’ve got the porter here to identify them.”

“Before you go,” said Thorndyke, “there are two little matters that I should like to settle.  One is the dagger:  it is in your pocket, I think.  May I have a look at it?”

The inspector rather reluctantly produced the dagger and handed it to my colleague.

“A very singular weapon, this,” said Thorndyke, regarding the dagger thoughtfully, and turning it about to view its different parts.  “Singular both in shape and material.  I have never seen an aluminium hilt before, and bookbinder’s morocco is a little unusual.”

“The aluminium was for lightness,” explained the inspector, “and it was made narrow to carry up the sleeve, I expect.”

“Perhaps so,” said Thorndyke.

He continued his examination, and presently, to the inspector’s delight, brought forth his pocket lens.

“I never saw such a man!” exclaimed the jocose detective.  “His motto ought to be, ‘We magnify thee.’  I suppose he’ll measure it next.”

The inspector was not mistaken.  Having made a rough sketch of the weapon on his block, Thorndyke produced from his bag a folding rule and a delicate calliper-gauge.  With these instruments he proceeded, with extraordinary care and precision, to take the dimensions of the various parts of the dagger, entering each measurement in its place on the sketch, with a few brief, descriptive details.

“The other matter,” said he at length, handing the dagger back to the inspector, “refers to the houses opposite.”

He walked to the window, and looked out at the backs of a row of tall buildings similar to the one we were in.  They were about thirty yards distant, and were separated from us by a piece of ground, planted with shrubs and intersected by gravel paths.

“If any of those rooms were occupied last night,” continued Thorndyke, “we might obtain an actual eyewitness of the crime.  This room was brilliantly lighted, and all the blinds were up, so that an observer at any of those windows could see right into the room, and very distinctly, too.  It might be worth inquiring into.”

“Yes, that’s true,” said the inspector; “though I expect, if any of them have seen anything, they will come forward quick enough when they read the report in the papers.  But I must be off now, and I shall have to lock you out of the rooms.”

As we went down the stairs, Mr. Marchmont announced his intention of calling on us in the evening, “unless,” he added, “you want any information from me now.”

“I do,” said Thorndyke.  “I want to know who is interested in this man’s death.”

“That,” replied Marchmont, “is rather a queer story.  Let us take a turn in that garden that we saw from the window.  We shall be quite private there.”