"I play the game for the game's own sake," said he. "But the problem certainly presents some points of interest, and I shall be very pleased to look into it. Some more facts, please."
"I have jotted down the more essential ones upon this sheet of paper, together with a few addresses which you will find of service. The actual official guardian of the papers is the famous government expert, Sir James Walter, whose decorations and sub-titles fill two lines of a book of reference. He has grown gray in the service, is a gentleman, a favoured guest in the most exalted houses, and, above all, a man whose patriotism is beyond suspicion. He is one of two who have a key of the safe. I may add that the papers were undoubtedly in the office during working hours on Monday, and that Sir James left for London about three o'clock taking his key with him. He was at the house of Admiral Sinclair at Barclay Square during the whole of the evening when this incident occurred."
"Has the fact been verified?"
"Yes; his brother, Colonel Valentine Walter, has testified to his departure from Woolwich, and Admiral Sinclair to his arrival in London; so Sir James is no longer a direct factor in the problem."
"Who was the other man with a key?"
"The senior clerk and draughtsman, Mr. Sidney Johnson. He is a man of forty, married, with five children. He is a silent, morose man, but he has, on the whole, an excellent record in the public service. He is unpopular with his colleagues, but a hard worker. According to his own account, corroborated only by the word of his wife, he was at home the whole of Monday evening after office hours, and his key has never left the watch-chain upon which it hangs."
"Tell us about Cadogan West."
"He has been ten years in the service and has done good work. He has the reputation of being hot-headed and imperious, but a straight, honest man. We have nothing against him. He was next Sidney Johnson in the office. His duties brought him into daily, personal contact with the plans. No one else had the handling of them."
"Who locked up the plans that night?"
"Mr. Sidney Johnson, the senior clerk."
"Well, it is surely perfectly clear who took them away. They are actually found upon the person of this junior clerk, Cadogan West. That seems final, does it not?"
"It does, Sherlock, and yet it leaves so much unexplained. In the first place, why did he take them?"
"I presume they were of value?"
"He could have got several thousands for them very easily."
"Can you suggest any possible motive for taking the papers to London except to sell them?"
"No, I cannot."
"Then we must take that as our working hypothesis. Young West took the papers. Now this could only be done by having a false key--"
"Several false keys. He had to open the building and the room."
"He had, then, several false keys. He took the papers to London to sell the secret, intending, no doubt, to have the plans themselves back in the safe next morning before they were missed. While in London on this treasonable mission he met his end."