"Are you hit badly?" he gasped through chattering teeth. "I'm not hit at all," muttered the doctor. "I stumbled and fell just as he fired. Look out! He's going to shoot again!" The rifle barrel came slowly into view through the loophole. Walter fired, but his bullet went wild. Carnes threw himself behind a rock for protection. * * * * * The rifle swung in Walter's direction and paused. As it did so, from the house came a strangled cry and a sound as of a blow. The rifle barrel disappeared, and the sounds of a struggle came from the building. "Come on!" cried Carnes as he rose to his feet, and made his stumbling way forward, the others following at the best speed which their numbed limbs would allow. As they reached the door they were aware of a struggle which was going on inside. With an oath the doctor threw his massive frame against the door. It creaked, but the solid oak of which it was composed was proof against the attack, and he drew back for another onslaught. From the house came a pistol shot, followed by a despairing cry and a guttural shout. Reinforced by Carnes, the doctor threw his weight against the door again. With a rending crash it gave, and they fell sprawling into the cabin. The doctor was the first one on his feet. "Who are you?" asked a voice from one corner. The doctor whirled like a flash and covered the speaker with his pistol. "Put them up!" he said tersely. "I am unarmed," the voice replied. "Who are you?" "We're from the United States Secret Service," replied Carnes who had gained his feet. "The game is up for you, and you'd better realize it." "Secret Service! Thank God!" cried the voice. "Get Koskoff--he has the plans. He has gone out through the tunnel!" "Where is it?" demanded Carnes. "The entrance is that iron plate on the floor." Carnes and the doctor jumped at the plate and tried to lift it, without result. There was no handle or projection on which they could take hold. "Not that way," cried the voice. "That cover is fastened on the inside. Go outside the building; he'll come out about two hundred yards north. Shoot him as he appears or he'll get away." The three men nearly tumbled over each other to get through the doorway into the bitter cold outside. As they emerged from the cabin the gaze of the guide swept the surrounding hills. "There he goes!" he cried. "Get him!" said Carnes sharply. Walter ran forward a few feet and dropped prone on the ground, cuddling the stock of his rifle to his cheek. Two hundred yards ahead a figure was scurrying over the rocks away from the cabin. Walter drew in his breath and his hand suddenly grew steady as his keen gray eyes peered through the sights. Carnes and the doctor held their breath in sympathy. * * * * * Suddenly the rifle spoke, and the fleeing man threw up his arms and fell forward on his face. "Got him," said Walter laconically.