“The Post Office,” Mr. Coulson continued meditatively, “is a great institution, both on your side and ours, but a letter posted in Washington has to go through a good many hands before it is delivered in London.”

Sir Edward smiled.

“It is a fact, sir,” he said, “which the various Governments of Europe have realized for many years, in connection with the exchange of communications one with the other.  Your own great country, as it grows and expands, becomes, of necessity, more in touch with our methods.  Did I understand that you have a letter for me, Mr. Coulson?”

Mr. Coulson produced it.

“Friend of mine you may have heard of,” he said, “asked me to leave this with you.  I am catching the Princess Cecilia from Southampton tomorrow.  I thought, perhaps, if I waited an hour or so, I might take the answer back with me.”

“It is getting late, Mr. Coulson,” Sir Edward reminded him, glancing at the clock.

Mr. Coulson smiled.

“I think, Sir Edward,” he said, “that in your line of business time counts for little.”

Sir Edward motioned his visitor to a chair and touched the bell.

“I shall require the A3X cipher, Sidney,” he said to his secretary.

Mr. Coulson looked up.

“Why,” he said, “I don’t think you’ll need that.  The letter you’ve got in your hand is just a personal one, and what my friend has to say to you is written out there in black and white.”

Sir Edward withdrew the enclosure from its envelope and raised his eyebrows.

“Isn’t this a trifle indiscreet?” he asked.

“Why, I should say not,” Mr. Coulson answered.  “My friend—­Mr. Jones we’ll call him—­knew me and, I presume, knew what he was about.  Besides, that is a plain letter from the head of a business firm to—­shall we say a client?  There’s nothing in it to conceal.”

“At the same time,” Sir Edward remarked, “it might have been as well to have fastened the flap of the envelope.”

Mr. Coulson held out his hand.

“Let me look,” he said.

Sir Edward gave it into his hands.  Mr. Coulson held it under the electric light.  There was no indication in his face of any surprise or disturbance.

“Bit short of gum in our stationery office,” he remarked.

Sir Edward was looking at him steadily.

“My impressions were,” he said, “when I opened this letter, that I was not the first person who had done so.  The envelope flew apart in my fingers.”

Mr. Coulson shook his head.

“The document has never been out of my possession, sir,” he said.  “It has not even left my person.  My friend Mr. Jones does not believe in too much secrecy in matters of this sort.  I have had a good deal of experience now and am inclined to agree with him.  A letter in a double-ended envelope, stuck all over with sealing wax, is pretty certain to be opened in case of any accident to the bearer.  This one, as you may not have noticed, is written in the same handwriting and addressed in the same manner as the remainder of my letters of introduction to various London and Paris houses of business.”