Rollo’s indifference had slipped from him completely.
“And next?” he demanded.
“I think we’ll set up the position on the big Chess-board before we go any further,” Westenhanger suggested. “I have a reason for that, as you’ll see.”
He went to the case holding the chessmen and set up the pieces one by one on the pavement squares. Then he returned to his seat and took up the document again.
“You see two white knights? Knight unto knight sheweth knowledge. That means, as I read it, that one knight can do something which the other knight can’t do. Very little examination shows what that thing is—it’s an unaided mate in four moves. Thus.”
He moved the one white knight successively from square to square until it reached the mating position on Queen’s Seventh. Eileen watched eagerly, expecting that this time something would happen, but she could detect nothing whatever. Westenhanger had noticed her attitude. He looked across the table at her with a smile.
“That’s what you saw me do yesterday. Now I’ll tell you what I was looking for.”
He turned to Rollo.
“You know that each of these pieces has a long spike on its base which slides into the holes in the Chess-board? On the surface it looks as if that had been designed merely to keep the pieces from being knocked over by anyone who has to walk among them in order to shift them from square to square. But I had at the back of my mind the idea of the old Corinthian as a man with a mechanical turn, and I put that idea alongside the notion of the spikes and the sequence of four fixed moves by the white knight. And so I reached the idea of . . .”
He looked interrogatively at his hearers, but neither of them had caught his meaning.