“And how,” Thorndyke asked as we sat at lunch, “has my learned friend progressed?  Does he propose that we advise Mr. Marchmont to enter a caveat?”

“I’ve read all the documents and boiled all the evidence down to a stiff jelly; and I am in a worse fog than ever.”

“There seems to be a slight mixture of metaphors in my learned friend’s remarks.  But never mind the fog, Jervis.  There is a certain virtue in fog.  It serves, like a picture frame, to surround the essential with a neutral zone that separates it from the irrelevant.”

“That is a very profound observation, Thorndyke,” I remarked ironically.

“I was just thinking so myself,” he rejoined.

“And if you could contrive to explain what it means—­”

“Oh, but that is unreasonable.  When one throws off a subtly philosophic obiter dictum one looks to the discerning critic to supply the meaning.  By the way, I am going to introduce you to the gentle art of photography this afternoon.  I am getting the loan of all the cheques that were drawn by Jeffrey Blackmore during his residence at New Inn—­there are only twenty-three of them, all told—­and I am going to photograph them.”

“I shouldn’t have thought the bank people would have let them go out of their possession.”

“They are not going to.  One of the partners, a Mr. Britton, is bringing them here himself and will be present while the photographs are being taken; so they will not go out of his custody.  But, all the same, it is a great concession, and I should not have obtained it but for the fact that I have done a good deal of work for the bank and that Mr. Britton is more or less a personal friend.”

“By the way, how comes it that the cheques are at the bank?  Why were they not returned to Jeffrey with the pass-book in the usual way?”

“I understand from Britton,” replied Thorndyke, “that all Jeffrey’s cheques were retained by the bank at his request.  When he was travelling he used to leave his investment securities and other valuable documents in his bankers’ custody, and, as he has never applied to have them returned, the bankers still have them and are retaining them until the will is proved, when they will, of course, hand over everything to the executors.”

“What is the object of photographing these cheques?” I asked.

“There are several objects.  First, since a good photograph is practically as good as the original, when we have the photographs we practically have the cheques for reference.  Then, since a photograph can be duplicated indefinitely, it is possible to perform experiments on it which involve its destruction; which would, of course, be impossible in the case of original cheques.”

“But the ultimate object, I mean.  What are you going to prove?”

“You are incorrigible, Jervis,” he exclaimed.  “How should I know what I am going to prove?  This is an investigation.  If I knew the result beforehand, I shouldn’t want to perform the experiment.”