Standing as it did in the battle zone; it had become little more than a ruin. Most of the thatched roof had been shot away, one side had gone altogether, and the other three sides leaned crazily toward each other. It was a little after midnight when Frank thought he saw a gleam of light either in the cabin or close by it. It was very faint, scarcely more than the glimmer of a firefly, and it vanished instantly. Still, it had been there. Cautiously, avoiding every twig with the stealth of an Indian, Frank crept toward the hut. CHAPTER XXI A FAMILIAR VOICE As Frank neared the cabin he redoubled his precautions, and it was here that his scout training stood him in good stead. When he was within twenty feet he went down flat on the earth and wormed his way to one of the sides that had been left standing. He placed his ear against a board and listened intently. But not a sound rewarded him. The deepest silence reigned. For a moment he was tempted to believe that his eyes had played a trick on him. But they had seldom done this and he had learned to trust them. The light could not have come from a firefly, for it was too late in the season for them. What then had caused it? He worked his way around to the shattered doorway and inch by inch lifted his head until his eyes were on a level with the floor. Quickly they swept the room, which was so small that the faint light that came from the stars enabled him to see that it was empty. When he was fully assured of this, he crept into the room and with his fingers explored every inch of the floor. The apartment was so small that this was not much of a task, and before long his hand came in contact with a match. It had been lighted and the softness of the charred end told him that this had been done recently. This then was the "firefly"! He continued his search with renewed caution and soon found a cartridge. He knew from the feel of it that it was of the kind used in the rifles with which the American troops were equipped. It was still warm, as though it had been recently in a belt close to a man's body. But what was a man doing in that lonely spot at that hour of the night? Was he a prowling spy from the German camp who had made a daring incursion into the American lines? He must solve the mystery. With every faculty at its highest pitch, he moved out into the open. A slight rustling in the forest near by fell on his ears. It might have been made by some woodland creature, but to his strained senses every sound, however slight, suggested a possible clue. He listened intently and heard it again, but this time it was a trifle louder than before. He rose to his feet and with catlike tread moved in the direction of the sound. As he drew hearer he heard it more plainly. And now his patience was rewarded, for he distinctly heard the low tone of a human voice.