"Stand back there. Keep the crowd back, Bill. We are getting amongst it. Sermons, as I live. Sermons. Was Mark's father a clergyman, or does Mark take to them naturally?"

"His father was a parson, I believe. Oh, yes, I know he was."

"Ah, then these are Father's books. 'Half-Hours with the Infinite' I must order that from the library when I get back. 'The Lost Sheep,' 'Jones on the Trinity,' 'The Epistles of St. Paul Explained.' Oh, Bill, we're amongst it. 'The Narrow Way, being Sermons by the Rev. Theodore Ussher' hal-LO!"

"What is the matter?"

"William, I am inspired. Stand by." He took down the Reverend Theodore Ussher's cla.s.sic work, looked at it with a happy smile for a moment, and then gave it to Bill.

"Here, hold Ussher for a bit."

Bill took the book obediently.

"No, give it me back. Just go out into the hall, and see if you can hear Cayley anywhere. Say 'Hallo' loudly, if you do."

Bill went out quickly, listened, and came back.

"It's all right."

"Good." He took the book out of its shelf again. "Now then, you can hold Ussher. Hold him in the left hand so. With the right or dexter hand, grasp this shelf firmly so. Now, when I say 'Pull,' pull gradually. Got that?"

Bill nodded, his face alight with excitement.

"Good." Antony put his hand into the s.p.a.ce left by the stout Ussher, and fingered the back of the shelf. "Pull," he said.

Bill pulled.

"Now just go on pulling like that. I shall get it directly. Not hard, you know, but just keeping up the strain."

His fingers went at it again busily.

And then suddenly the whole row of shelves, from top to bottom, swung gently open towards them.

"Good Lord!" said Bill, letting go of the shelf in his amazement.

Antony pushed the shelves back, extracted Ussher from Bill's fingers, replaced him, and then, taking Bill by the arm, led him to the sofa and deposited him in it. Standing in front of him, he bowed gravely.

"Child's play, Watson," he said; "child's play."

"How on earth-"

Antony laughed happily and sat down on the sofa beside him.

"You don't really want it explained," he said, smacking him on the knee; "you're just being Watsonish. It's very nice of you, of course, and I appreciate it."

"No, but really, Tony."

"Oh, my dear Bill!" He smoked silently for a little, and then went on, "It's what I was saying just now--a secret is a secret until you have discovered it, and as soon as you have discovered it, you wonder why everybody else isn't discovering it, and how it could ever have been a secret at all. This pa.s.sage has been here for years, with an opening at one end into the library, and at the other end into the shed. Then Mark discovered it, and immediately he felt that everybody else must discover it. So he made the shed end more difficult by putting the croquet-box there, and this end more difficult by-" he stopped and looked at the other "by what, Bill?"

But Bill was being Watsonish.

"What?"

"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 n.o.body 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 n.o.body 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 pa.s.sage 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 pa.s.sage, 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?"