“Of a combination lock!” he concluded, after a pause. “Your grandfather was more of a mechanic than you gave him credit for. As I understand the machine—of course, this is only guess-work—under each hole in the four squares of the knight’s moves there lies the end of a lever. When you drop the knight into its place on the square, the spike depresses the lever. The whole secret of the thing is that the four levers must be depressed in that particular sequence. That guards against the lock being sprung in the course of normal play. The chances against that combination are considerable; and I expect some of the other pieces also depress lock-levers, so that it’s almost impossible that the thing should be unlocked by a chance game. In fact, the whole affair is simply a clumsy forerunner of the ordinary dial lock on good safes.”
“Yes, but it hasn’t opened!” commented Eileen.
“It has unlocked something, though,” Westenhanger retorted. “That was what puzzled me yesterday when apparently nothing happened after I’d played the moves. But the Corinthian was taking no chances. The Chess-board is the lock, but the thing it secures is somewhere else.”
“That sounds nonsense to me,” Eileen said, decidedly.
Westenhanger smiled with a touch of friendly maliciousness.
“We’ve still two things which we haven’t used. This is where I went wrong yesterday, Eileen,” he interjected. “There’s another text, and there’s the leather disc. Take the text first of all. Where your treasure is, there will your heart be also. Remember the pun in the first case? There’s another one here. I didn’t spot it for a while.”
He challenged Eileen’s ingenuity with a look across the table and left her to puzzle the thing out for herself.
“Not see it? I’ll give you a clue. ‘As pants the hart for cooling streams . . .’ ”
He caught her eye and his glance led her gaze round the room till it came to the tapestry of Diana’s hunting.
“Oh, now I see!” she cried. “You mean there’s something hidden behind that stag—the hart—in the arras!”