“Stop a bit,” said Spargo.  “Where did he take the key from with which he unlocked the box?”

“It was one of several which he carried on a split ring, and he took the bunch out of his left-hand trousers pocket,” replied Mr. Criedir.  “Oh, I keep my eyes open, young gentleman!  Well—­he opened his box.  It seemed to me to be full of papers—­at any rate there were a lot of legal-looking documents on the top, tied up with red tape.  To show you how I notice things I saw that the papers were stained with age, and that the red tape was faded to a mere washed-out pink.”

“Good—­good!” murmured Spargo.  “Excellent!  Proceed, sir,’’

“He put his hand under the topmost papers and drew out an envelope,” continued Mr. Criedir.  “From the envelope he produced an exceedingly rare, exceedingly valuable set of Colonial stamps—­the very-first ever issued.  ‘I’ve just come from Australia,’ he said.  ’I promised a young friend of mine out there to sell these stamps for him in London, and as I was passing this way I caught sight of your shop.  Will you buy ’em, and how much will you give for ’em?’”

“Prompt,” muttered Spargo.

“He seemed to me the sort of man who doesn’t waste words,” agreed Mr. Criedir.  “Well, there was no doubt about the stamps, nor about their great value.  But I had to explain to him that I was retiring from business that very day, and did not wish to enter into even a single deal, and that, therefore, I couldn’t do anything.  ‘No matter,’ he says, ’I daresay there are lots of men in your line of trade—­perhaps you can recommend me to a good firm?’ ’I could recommend you to a dozen extra-good firms,’ I answered.  ’But I can do better for you.  I’ll give you the name and address of a private buyer who, I haven’t the least doubt, will be very glad to buy that set from you and will give you a big price.’  ‘Write it down,’ he says, ‘and thank you for your trouble.’  So I gave him a bit of advice as to the price he ought to get, and I wrote the name and address of the man I referred to on the back of one of my cards.”

“Whose name and address?” asked Spargo.

“Mr. Nicholas Cardlestone, 2, Pilcox Buildings, Middle Temple Lane,” replied Mr. Criedir.  “Mr. Cardlestone is one of the most enthusiastic and accomplished philatelists in Europe.  And I knew he didn’t possess that set of stamps.”

“I know Mr. Cardlestone,” remarked Spargo.  “It was at the foot of his stairs that Marbury was found murdered.”

“Just so,” said Mr. Criedir.  “Which makes me think that he was going to see Mr. Cardlestone when he was set upon, murdered, and robbed.”

Spargo looked fixedly at the retired stamp-dealer.

“What, going to see an elderly gentleman in his rooms in the Temple, to offer to sell him philatelic rarities at—­past midnight?” he said.  “I think—­not much!”

“All right,” replied Mr. Criedir.  “You think and argue on modern lines—­which are, of course, highly superior.  But—­how do you account for my having given Marbury Mr. Cardlestone’s address and for his having been found dead—­murdered—­at the foot of Cardlestone’s stairs a few hours later?”