the pound of its hoofs echoing through

  Without a word the two Policemen separated and dropped into the shadows on either side of the shaft of light from the doorway.   "Go into the other room, Helen." Mahon's order was sharp and low.   On came the racing horse, the pound of its hoofs echoing through the trees like the charge of a troop, filling the vast silence with piercing fancies. Echo and hoof-beats grew louder and louder; there was no other sound. At the edge of the village the horse turned from the clearing along the grade into the main street, and the echo, sharpened now by crowding walls, sent the blood tingling through the Sergeant's veins.   Over the pounding hoofs broke a muttering voice.   In another five seconds the horse would cross the shaft of light. Mahon and Williams raised their guns. The former edged out toward the narrow path. He had no thought of warning the man--he wished to see him dash into that shaft of light, that eyes might come to the aid of ears. Another moment. . . .   With a slithering of hoofs the horse pulled up in mid-flight at the very edge of the beams. A voice, husky with anxiety, shouted:   "Sergeant, Sergeant Mahon! Quick! For God's sake!"   At the first sound Mahon felt the blood rush to his head. His knees shook. His left hand groped to his forehead. Then he wrenched himself back to his duty.   "What is it?" His voice was quiet, but he avoided the light.