“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.”

An hour later Holmes, Lestrade and I stood upon the Underground railroad at the point where it emerges from the tunnel immediately before Aldgate Station. A courteous red-faced old gentleman represented the railway company.

“This is where the young man’s body lay,” said he, indicating a spot about three feet from the metals. “It could not have fallen from above, for these, as you see, are all blank walls. Therefore, it could only have come from a train, and that train, so far as we can trace it, must have passed about midnight on Monday.”

“Have the carriages been examined for any sign of violence?”

“There are no such signs, and no ticket has been found.”

“No record of a door being found open?”

“None.”

“We have had some fresh evidence this morning,” said Lestrade. “A passenger who passed Aldgate in an ordinary Metropolitan train about 11:40 on Monday night declares that he heard a heavy thud, as of a body striking the line, just before the train reached the station. There was dense fog, however, and nothing could be seen. He made no report of it at the time. Why, whatever is the matter with Mr. Holmes?”

My friend was standing with an expression of strained intensity upon his face, staring at the railway metals where they curved out of the tunnel. Aldgate is a junction, and there was a network of points. On these his eager, questioning eyes were fixed, and I saw on his keen, alert face that tightening of the lips, that quiver of the nostrils, and concentration of the heavy, tufted brows which I knew so well.

“Points,” he muttered; “the points.”

“What of it? What do you mean?”

“I suppose there are no great number of points on a system such as this?”

“No; there are very few.”

“And a curve, too. Points, and a curve. By Jove! if it were only so.”

“What is it, Mr. Holmes? Have you a clue?”

“An idea - an indication, no more. But the case certainly grows in interest. Unique, perfectly unique, and yet why not? I do not see any indications of bleeding on the line.”

“There were hardly any.”

“But I understand that there was a considerable wound.”

“The bone was crushed, but there was no great external injury.”

“And yet one would have expected some bleeding. Would it be possible for me to inspect the train which contained the passenger who heard the thud of a fall in the fog?”

“I fear not, Mr. Holmes. The train has been broken up before now, and the carriages redistributed.”

“I can assure you, Mr. Holmes,” said Lestrade, “that every carriage has been carefully examined. I saw to it myself.”

It was one of my friend’s most obvious weaknesses that he was impatient with less alert intelligences than his own.