But Bill was being Watsonish.

“What?”

“Obviously by rearranging 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 rearranged 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.”