“Obviously by re-arranging his books. He happened to take out ‘The Life of Nelson’ or ‘Three Men in a Boat,’ or whatever it was, and by the merest chance discovered the secret. Naturally he felt that everybody else would be taking down ‘The Life of Nelson’ or ‘Three Men in a Boat.’ Naturally he felt that the secret would be safer if nobody ever interfered with that shelf at all. When you said that the books had been re-arranged a year ago—just about the time the croquet-box came into existence—of course, I guessed why. So I looked about for the dullest books I could find, the books nobody ever read. Obviously the collection of sermon-books of a mid-Victorian clergyman was the shelf we wanted.” “Yes, I see. But why were you so certain of the particular place?” “Well, he had to mark the particular place by _some_ book. I thought that the joke of putting ‘The Narrow Way’ just over the entrance to the passage might appeal to him. Apparently it did.” Bill nodded to himself thoughtfully several times. “Yes, that’s very neat,” he said. “You’re a clever devil, Tony.” Tony laughed. “You encourage me to think so, which is bad for me, but very delightful.” “Well, come on, then,” said Bill, and he got up, and held out a hand. “Come on where?” “To explore the passage, of course.” Antony shook his head. “Why ever not?” “Well, what do you expect to find there?” “I don’t know. But you seemed to think that we might find something that would help.” “Suppose we find Mark?” said Antony quietly. “I say, do you really think he’s there?” “Suppose he is?” “Well, then, there we are.” Antony walked over to the fireplace, knocked out the ashes of his pipe, and turned back to Bill. He looked at him gravely without speaking. “What are you going to say to him?” he said at last. “How do you mean?” “Are you going to arrest him, or help him to escape?” “I—I—well, of course, I—” began Bill, stammering, and then ended lamely, “Well, I don’t know.” “Exactly. We’ve got to make up our minds, haven’t we?” Bill didn’t answer. Very much disturbed in his mind, he walked restlessly about the room, frowning to himself, stopping now and then at the newly discovered door and looking at it as if he were trying to learn what lay behind it. Which side was he on, if it came to choosing sides—Mark’s or the Law’s? “You know, you can’t just say, ‘Oh—er—hallo!’ to him,” said Antony, breaking rather appropriately into his thoughts. Bill looked up at him with a start. “Nor,” went on Antony, “can you say, ‘This is my friend Mr. Gillingham, who is staying with you. We were just going to have a game of bowls.’”