“He has been ten years in the service and has done good work. He has the reputation of being hot-headed and impetuous, 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 the plans up 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.”

“How?”

“We will suppose that he was travelling back to Woolwich when he was killed and thrown out of the compartment.”

“Aldgate, where the body was found, is considerably past the station for London Bridge, which would be his route to Woolwich.”

“Many circumstances could be imagined under which he would pass London Bridge. There was someone in the carriage, for example, with whom he was having an absorbing interview. This interview led to a violent scene in which he lost his life. Possibly he tried to leave the carriage, fell out on the line, and so met his end. The other closed the door. There was a thick fog, and nothing could be seen.”

“No better explanation can be given with our present knowledge; and yet consider, Sherlock, how much you leave untouched. We will suppose, for argument’s sake, that young Cadogan West had determined to convey these papers to London. He would naturally have made an appointment with the foreign agent and kept his evening clear. Instead of that he took two tickets for the theatre, escorted his fiancee halfway there, and then suddenly disappeared.”

“A blind,” said Lestrade, who had sat listening with some impatience to the conversation.

“A very singular one. That is objection No. 1. Objection No. 2: We will suppose that he reaches London and sees the foreign agent. He must bring back the papers before morning or the loss will be discovered. He took away ten. Only seven were in his pocket. What had become of the other three? He certainly would not leave them of his own free will. Then, again, where is the price of his treason? One would have expected to find a large sum of money in his pocket.”

“It seems to me perfectly clear,” said Lestrade. “I have no doubt at all as to what occurred. He took the papers to sell them. He saw the agent. They could not agree as to price. He started home again, but the agent went with him. In the train the agent murdered him, took the more essential papers, and threw his body from the carriage. That would account for everything, would it not?”

“Why had he no ticket?”

“The ticket would have shown which station was nearest the agent’s house. Therefore he took it from the murdered man’s pocket.”