It was quickly manifested that the garrison lookout had become aware of the aërial visitation, and that they did not approve of the color of the hovering aircraft. A couple of smokeballs ascended and burst in the center of a cloudrack far to the right of the machine. Renos broke his record for silence with a shrill cackle. "Save your powder, you numbskulls," he shouted for his own satisfaction. Roque seemed oblivious of the gunplay below. As the biplane described great circles over the fort, he kept his glasses steadily aimed at a point in the enclosure over which the flag was floating. The men who emerged from the officers' quarters all wore the French uniform. Roque had evidently cleared up a disturbing point in his mind as he muttered something about a "fool story," and "I might have known there was nothing to it." Having satisfied himself that it was still an independent little war at this remote point from the main field of operations, and that he had been misled by some advices previously received, the chief observer passed the word to his pilot to back-track, at the same time giving signal to the companion biplane. As the machines swung around for the return flight, and drew closer together, Renos gave a megaphone yell through a hollow formed by his hands: "Speed for your lives, they're on the wing!" Above the gentle slopes on the west, leading to the summit of the mountain ranges, aircraft had arisen, looking, at a distance, like black dragonflies. At the same moment, the invading biplanes also had a reminder to hurry from the fortress they were leaving behind. A shell burst seemingly quite close to the machine Henri was driving, and the craft dipped far to one side. Billy's heart beat up to his throat when he saw the break in the flight. But his was an exulting cry when the momentarily stricken flyer righted, and bored ahead. "Glory be!" hoarsely rejoiced the boy from Bangor, when his chum again drew to the upper level. Seventy miles an hour was the clip of the fleeing biplanes, and no less speedy the onrush of the aircraft from the slopes. "Steady, and a little to the right," Renos instructed Henri. The observer was resting the rifle barrel on the rigging, awaiting a broadside target. Sping! One of the attacking aviators was first with his rifle, and the bullet nicked the armored side of the German craft. Sput! Henri heard an angry exclamation behind him, and shifted an eye long enough to see that Renos was nursing a bloody wrist on his knee. "How hard are you hit?" was the anxious question of the young pilot. "Nothing to kill," replied the observer, as he used his uninjured fingers and his teeth in knotting a handkerchief above the wound so as to compress the severed artery. With the utmost calm he then deliberately used his left hand in rifle aiming, and sent a bullet into the nearest hostile machine.