But, as the minutes slipped by, and only the moaning of the wind broke the silence of the night, the lad grew ashamed of his fears. The bitter cold was the only enemy he had to contend with. His bare ears and hands pained him terribly, and a slight sensation of drowsiness warned him that he must keep moving. So he stood his musket against a big apple tree, wrapping a rag around the flint and pan to protect them from the damp, and began to pace up and down the narrow angle of the orchard. He continued this for a quarter of an hour, stopping occasionally to look and listen, until his feet had trodden a well-defined path between the trees. Feeling the need of more violent exercise, he rapidly folded and unfolded his arms for a few minutes, and then, fastening his hands on a big limb overhead, he repeatedly drew his chin up to a level with it. When he had warmed himself comfortably by these means he shouldered his musket and stepped to the fence. "Why don't Barnabas come?" he said half aloud. "I've surely been here half an hour, and that was the limit. By this time the grain ought to be all loaded and on the way to camp. I wouldn't mind the cold if there was any fighting going on, but this sentry duty in winter is the worst part of a soldier's life. And I am anxious to get back to see how my father is--" The sentence was stifled on the lad's lips, and he very nearly uttered a sharp cry. For just then, under one of the shuttered windows of the house, he saw a flash of yellow light. It was visible for a few seconds, and then it vanished as mysteriously as it had appeared. Nathan felt a cold shiver run down his back. "Did I imagine that light?" he asked himself, "or is there some one in the house?" The next instant he was crouching low behind the fence, every nerve quivering with excitement, and his musket trembling in his hands. He had made another startling discovery, and one that was too real to be doubted. The dark figure of a man was approaching the rear of the house from the direction of the American lines, and it was only too evident that he was not one of Corporal Dubbs's sentries. On he came through the drifted snow, stepping quickly but stealthily, and turning his head from right to left. Nathan aimed his musket through the fence. "A spy!" he muttered. "He's just been to the camp! Shall I shoot?" putting his finger to the trigger. "No, I have a better plan. He's going to the house, and there he'll be trapped." The lad was right. A moment later the crouching figure had gained the rear wall and was lost to sight. A door was heard to softly open and close.