He wiped his brow at the recollection, and the inspector smiled appreciatively.

“And that was the last of them?” said the latter; and as the porter nodded sulkily, he asked:  “Should you recognize the note that the Italian gave you?”

“I should,” answered the porter with frosty dignity.

The inspector bustled out of the room, and returned a minute later with a letter-case in his hand.

“This was in his breast-pocket,” said he, laying the bulging case on the table, and drawing up a chair.  “Now, here are three letters tied together.  Ah! this will be the one.”  He untied the tape, and held out a dirty envelope addressed in a sprawling, illiterate hand to “Mr. Hartridge, Esq.”  “Is that the note the Italian gave you?”

The porter examined it critically.  “Yes,” said he; “that is the one.”

The inspector drew the letter out of the envelope, and, as he opened it, his eyebrows went up.

“What do you make of that, Doctor?” he said, handing the sheet to Thorndyke.

Thorndyke regarded it for a while in silence, with deep attention.  Then he carried it to the window, and, taking his lens from his pocket, examined the paper closely, first with the low power, and then with the highly magnifying Coddington attachment.

“I should have thought you could see that with the naked eye,” said the inspector, with a sly grin at me.  “It’s a pretty bold design.”

“Yes,” replied Thorndyke; “a very interesting production.  What do you say, Mr. Marchmont?”

The solicitor took the note, and I looked over his shoulder.  It was certainly a curious production.  Written in red ink, on the commonest notepaper, and in the same sprawling hand as the address, was the following message:  “You are given six days to do what is just.  By the sign above, know what to expect if you fail.”  The sign referred to was a skull and crossbones, very neatly, but rather unskilfully, drawn at the top of the paper.

“This,” said Mr. Marchmont, handing the document to Mr. Curtis, “explains the singular letter that 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!”