"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 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? Once 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."
"Good, Lestrade, very good," said Holmes. "Your theory holds together. But if this is true, then the case is at an end. On the one hand, the traitor is dead. On the other, the plans of the Bruce-Partington submarine are presumably already on the Continent. What is there for us to do?"
"To act, Sherlock--to act!" cried Mycroft, springing to his feet. "All my instincts are against this explanation. Use your powers! Go to the scene of the crime! See the people concerned! Leave no stone unturned! In all your career you have never had so great a chance of serving your country."
"Well, well!" said Holmes, shrugging his shoulders. "Come, Watson! And you, Lestrade, could you favour us with your company for an hour or two? We will begin our investigation by a visit to Aldgate Station. Good-bye, Mycroft. I shall let you have a report before evening, but I warn you in advance that you have little to expect."