"Let her go, then," said Hal, and the single guard who had remained gave the machine momentum with a vigorous push. The machine moved slowly across the ground at first, then, under Hal’s guiding hand, dashed on swifter and swifter. Hal touched the elevating lever and the airplane soared into the air. Now Chester had been aloft many times, but he had never reached a point where he was not affected by the sensation of the earth dropping away from him. For a moment he clung to the side of the car. His head cleared, in a twinkling, however, and he breathed a sigh of relief. "All right, Chester," Hal called back, not taking the time to turn his head. "All right," was Chester’s reply. "Step on her, Hal." Hal obeyed this injunction, and the plane darted in the direction of the distant enemy like a big bird. There was no light aboard the craft that carried the two lads toward the German lines. On either side, above and below, however, Hal could see now. and then a faint twinkle, indicating that other American craft, bent upon no such dangerous mission as Hal and Chester, still were on the alert to prevent a possible surprise attack by the foe. These lights were soon gone, however, and now all that Chester could see was the faint outline of Hal’s head before him. He looked back, but the last of the American lights had been lost in the distance. Ahead, the German lines were still too far distant for a plane to be distinguishable should it be on guard aloft. The night was very dark. For this Hal felt thankful, for it meant that, barring accidents and the rays of German searchlights, he had more opportunity of guiding his craft into the enemy lines, unobserved. Could he escape the prying eyes of the foe’s sentinels of the sky, he felt that he had nothing to fear. The distance between the German and allied lines at that point, Hal knew, was less than three-quarters of a mile. This distance was covered in a jiffy, but still Hal kept the nose of the craft pointed due east, for it was his intention to come down well within the foe’s lines rather than to risk a landing near the front. But at last he felt he had gone far enough. His hand tightened on the controls and gradually the speed of the plane slackened. Chester leaned forward, and putting his mouth close to Hal’s ears, exclaimed: "Going down here?" "Yes," was Hal’s reply. "May as well, I guess. It should be as safe as any place. Suit you?" Chester shrugged in the darkness. "I’m satisfied if you are," he replied. "Shoot!" The plane began to descend. *CHAPTER III* *AMONG THE ENEMY* The aircraft settled to earth in the darkness as gently as a huge bird and Hal and Chester stepped out silently. For a moment they stood trying to get their bearings. "Where do you figure we are?" asked Chester in a low tone. "We should be a mile due east of Sedan," was Hal’s reply. "I saw the lights of the city below as we passed."