“My poor Louis!” said Carrados, in friendly ridicule.  “You were at the end of your tether?”

“I was,” admitted Carlyle.  “And now that you know the sort of job it is I don’t suppose that you are keen on wasting your time over it.”

“That would hardly be fair, would it?” said Carrados reasonably.  “No, Louis, I will take over your honest old driver and your greasy young signalman and your fatal signal that cannot be seen from anywhere.”

“But it is an important point for you to remember, Max, that although the signal cannot be seen from the box, if the mechanism had gone wrong, or anyone tampered with the arm, the automatic indicator would at once have told Mead that the green light was showing.  Oh, I have gone very thoroughly into the technical points, I assure you.”

“I must do so too,” commented Mr. Carrados gravely.

“For that matter, if there is anything you want to know, I dare say that I can tell you,” suggested his visitor.  “It might save your time.”

“True,” acquiesced Carrados.  “I should like to know whether anyone belonging to the houses that bound the line there came of age or got married on the twenty-sixth of November.”

Mr. Carlyle looked across curiously at his host.

“I really do not know, Max,” he replied, in his crisp, precise way.  “What on earth has that got to do with it, may I inquire?”

“The only explanation of the Pont St. Lin swing-bridge disaster of ’75 was the reflection of a green bengal light on a cottage window.”

Mr. Carlyle smiled his indulgence privately.

“My dear chap, you mustn’t let your retentive memory of obscure happenings run away with you,” he remarked wisely.  “In nine cases out of ten the obvious explanation is the true one.  The difficulty, as here, lies in proving it.  Now, you would like to see these men?”

“I expect so; in any case, I will see Hutchins first.”

“Both live in Holloway.  Shall I ask Hutchins to come here to see you—­say to-morrow?  He is doing nothing.”

“No,” replied Carrados.  “To-morrow I must call on my brokers and my time may be filled up.”

“Quite right; you mustn’t neglect your own affairs for this—­experiment,” assented Carlyle.

“Besides, I should prefer to drop in on Hutchins at his own home.  Now, Louis, enough of the honest old man for one night.  I have a lovely thing by Eumenes that I want to show you.  To-day is—­Tuesday.  Come to dinner on Sunday and pour the vials of your ridicule on my want of success.”

“That’s an amiable way of putting it,” replied Carlyle.  “All right, I will.”

Two hours later Carrados was again in his study, apparently, for a wonder, sitting idle.  Sometimes he smiled to himself, and once or twice he laughed a little, but for the most part his pleasant, impassive face reflected no emotion and he sat with his useless eyes tranquilly fixed on an unseen distance.  It was a fantastic caprice of the man to mock his sightlessness by a parade of light, and under the soft brilliance of a dozen electric brackets the room was as bright as day.  At length he stood up and rang the bell.