“But the thing is impossible, Thorndyke,” I said.  “Not only did the witnesses recognize their own signatures and the painter’s greasy finger-marks, but they had both read the will and remembered its contents.”

“Yes; that is the interesting feature in the case.  It is a very pretty problem.  I shall give you a last chance to solve it.  To-morrow evening we shall have to give a full explanation, so you have another twenty-four hours in which to think it over.  And, meanwhile, I am going to take you to my club to dine.  I think we shall be pretty safe there from Mrs. Schallibaum.”

He sat down and wrote a letter, which was apparently quite a short one, and having addressed and stamped it, prepared to go out.

“Come,” said he, “let us away to ’the gay and festive scenes and halls of dazzling light.’  We will lay the mine in the Fleet Street pillar box.  I should like to be in Marchmont’s office when it explodes.”

“I expect, for that matter,” said I, “that the explosion will be felt pretty distinctly in these chambers.”

“I expect so, too,” replied Thorndyke; “and that reminds me that I shall be out all day to-morrow, so, if Marchmont calls, you must do all that you can to persuade him to come round after dinner and bring Stephen Blackmore, if possible.  I am anxious to have Stephen here, as he will be able to give us some further information and confirm certain matters of fact.”

I promised to exercise my utmost powers of persuasion on Mr. Marchmont which I should certainly have done on my own account, being now on the very tiptoe of curiosity to hear Thorndyke’s explanation of the unthinkable conclusion at which he had arrived—­and the subject dropped completely; nor could I, during the rest of the evening, induce my colleague to reopen it even in the most indirect or allusive manner.

Our explanations in respect of Mr. Marchmont were fully realized; for, on the following morning, within an hour of Thorndyke’s departure from our chambers, the knocker was plied with more than usual emphasis, and, on my opening the door, I discovered the solicitor in company with a somewhat older gentleman.  Mr. Marchmont appeared somewhat out of humour, while his companion was obviously in a state of extreme irritation.

“How d’you do, Dr. Jervis?” said Marchmont as he entered at my invitation.  “Your friend, I suppose, is not in just now?”

“No; and he will not be returning until the evening.”

“Hm; I’m sorry.  We wished to see him rather particularly.  This is my partner, Mr. Winwood.”

The latter gentleman bowed stiffly and Marchmont continued: 

“We have had a letter from Dr. Thorndyke, and it is, I may say, a rather curious letter; in fact, a very singular letter indeed.”

“It is the letter of a madman!” growled Mr. Winwood.

“No, no, Winwood; nothing of the kind.  Control yourself, I beg you.  But really, the letter is rather incomprehensible.  It relates to the will of the late Jeffrey Blackmore—­you know the main facts of the case; and we cannot reconcile it with those facts.”