WITH the arrival of the biplanes from the factory, the Boy Aviators were kept busy with brief test flights over valley and plain, awaiting the convenience of Roque for the wider sweep he was planning. It developed that the boys were expected to navigate separately on this occasion, Billy to pilot Roque himself, and Henri to be accompanied by one Renos, who had been awarded a service badge of honor for his work as an aërial observer in giving first warning of the advance of a French division against Burnhaupt, which saved the day for the Germans. "The seaplane is the rig for weight carrying," exclaimed Roque, in accounting for this assignment, "but these machines, as you know, are solely in the speed class, and it is many chances to one that we will be compelled to tax every ounce of power before we get through. So we have no use for deadwood." Renos, who was to sit behind Henri, was the silent man of the expedition, as far as talking was concerned, but when it came to be up and doing he could be counted on to the limit. He was a human route-box of the Sundgau, the fighting territory, and very much at home in a flying machine. When the two machines one morning flew over the German frontier, in compliance with the "ready" order of Roque, Renos' knees were crossed by a wicked-looking rifle, and of the party he was the only one armed. Billy, observing this war-like figure, asked Roque if he expected to get into close quarters on this trip. "Not unless some of the bomb-throwing crowd that scarred the landscape the other night should cross our path," replied the secret agent. As Renos was the qualified guide, the biplane bearing him went to the front, and Henri received overshoulder directions as to the course to be maintained. The apparent reason why the German expert did not pilot the craft himself was that he wanted a loose hand in case of emergency, and a free eye for the panorama below. He was satisfied, too, that one as good as the best was doing the steering. Henri was instructed to keep a respectful distance from the near mountain peaks, where the French had mounted artillery, for one round from these guns, close enough, would have ended the flight and the flyers there and then. But Roque and Renos kept constant vigil with glasses, and Billy wondered that the pair did not get a crick in the neck with all the head-turning they did. A sharp order advised the pilots to send the biplanes farther aloft, and circle. The French fortress of Belfort could be seen directly underneath. The aviators well knew that an explosion close to an aëroplane is often sufficient, through the force of the air concussion alone, to bring it down, and they knew they could not chance a close shot from the long-range guns in the fort. Though the machines now evoluted at greater height, the powerful glasses enabled the observers to plainly distinguish the movements below.