he wrote yesterday. You have it with
you, I think?"

"Yes," replied Mr. Curtis; "here it is."

He produced a letter from his pocket, and read aloud:

"'Yes: come if you like, though it is an ungodly hour. Your
threatening letters have caused me great amusement. They are worthy
of Sadler's Wells in its prime.

"'ALFRED HARTRIDGE.'"

"Was Mr. Hartridge ever in Italy?" asked Inspector Badger.

"Oh yes," replied Mr. Curtis. "He stayed at Capri nearly the whole of
last year."

"Why, then, that gives us our clue. Look here. Here are these two other
letters; E.C. postmark--Saffron Hill is E.C. And just look at that!"

He spread out the last of the mysterious letters, and we saw that,
besides the _memento mori_, it contained only three words: "Beware!
Remember Capri!"

"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