The Case of the Black Twenty-Two by Brian Flynn

Peter whistled. "You seem pretty sure of it. But all the same -- "

Anthony interrupted him a trifle impatiently. "Those little mud pellets and small stones told me an unmistakable story. It seemed to me a most important factor in the case-remember no weapon was found near the body. It was obvious that Stewart had been struck from behind-I immediately deduced a sharp and heavy piece of stone. But if it hadn't been for the proximity of the ink-bowl to the dead man's head, the true significance would probably have escaped me. For the wound on the head was clean-I inquired of the doctor through Goodall. The murderer held the piece of stone by the ‘neck' end-soil side uppermost-and struck Stewart with the comparatively clean part, and the force of the blows caused the small stones underneath (as they lay originally) to be dislodged. " He held out the weapon to Daventry. "Of course the water in the pool has cleaned it, but I daresay a thorough and scientific examination may yield us some little evidences to support my theory. Time will tell-we'll take it back to the library and hand it over to Goodall upon his return from London, as a souvenir. " He turned to Peter. "But not a word till I say when."