And he had made no mistake! For as he closed the circuit, he saw a flash of flame at the spot where he and Henri had dug the hole into which the petrol had flowed from the barrel they had opened. The spark had fired the explosive gas that results when petrol is mixed with air. The flame ran along the shallow trench, and, amid a chorus of shrieks from the Germans who scattered in all directions, the fire reached the barrel. In a moment there was a loud explosion. The flame flew to the other barrels--the whole neighborhood of the barrels, owing to the mixture of the petrol and the air, was then filled with an explosive and inflammable gas. There was a great flash of flame, broken by a dozen sharp reports as one barrel after another blew up. And still, though the Germans were flying in all directions, plainly visible in the light of the blazing gasoline, the real success of Frank's plan hung in the balance. But then what he had calculated happened. The flame ran through the lines of hose. And a moment later two great shafts of flame marked the spread of the fire to the helpless monsters of the air. There was no chance to save them. Indeed, even the Germans had no other thought than to save their own lives. Their raid, whatever its ultimate object, was ruined and two vessels of the great air fleet of the Kaiser were destroyed. For a moment after the final catastrophe the two scouts stayed, caught by the wonder and the magnificence of the ruin they had wrought. But then Frank cried out, "Come on! We haven't a moment to lose! They'll know that that was no accident! Some came running this way. They'll find the wires! And then they'll know. The wires will bring them here. Hurry!" They began running desperately toward the automobile. CHAPTER XVII THE ESCAPE Their one chance of escape, as they both realized fully, was to get back to their automobile before the Germans recovered themselves sufficiently to begin searching for those who had brought such swift and terrible disaster upon their enterprise. And so they made no effort to move quietly or secretly now. To do so would have meant delay and delay was what they could not afford. The distance seemed far greater than when they had first traversed it. It seemed that they would never pass the house which the Germans had used as a base. But finally they reached it. And as they did so a door burst open, and they saw a light within. A man, with the cap of a German officer, though otherwise he wore civilian clothes, came rushing out, tugging at his pistol. He had heard them running. By some bad chance, then, there had been a man--a German--left in the inn! "Stop!" he cried, furiously. But they kept on running. He could not see them, dazzled as he was by coming from the lighted house into the deep darkness of the road. But he was in front of them, and they slowed up, instinctively, though they still ran. And then they came into the light of the door. He started back.