Buck was climbing, not too fast, for he watched, still hoping that something might happen that he would sight Blaine again. Flying thus easily, climbing still higher, he was all at once startled by a burst of machine gun fire from the ground ahead. There came a reply higher up, and he felt that this must come from Lafe. Mounting swiftly, he presently became conscious that a machine was hovering above and behind, "getting on his tail" as the slang runs among aviators at the front. The quickest way to avert the danger was first to try the "side loop" which is a kind of "loop-the-loop" sideways, a risky trick, yet a good thing if rightly done. Buck tried it instantly. When upside down he darted ahead swiftly but in a reversed course, bringing him fairly behind the other plane as he, righted. As he came up to a level again, now behind his opponent, he saw for an instant that the shadow looming scarce fifty yards ahead looked strangely like Blaine's machine. What to do next -- before firing? Use his private signal, of course. No sooner thought than done. Two peculiar flares shot forth, each glowing brightly for an instant, then vanishing. "But -- hey?" Bangs was ejaculating to himself excitedly. "Will he answer?" Up, up climbed Buck, his pulses throbbing for one long instant, the nose of his machine settling rapidly on the tail of the other plane. Then came an answering flash. After that another. "Bully for you, Lafe! My, that was a close call! I mustn't lose track of him again. We'll be there with the goods yet, if we stick together." This to himself. Presently both machines were moving side by side, hardly fifty yards apart. To come closer at this rate of speed these small scouting planes maintaining would have caused a mutual air suction that might cause a collision. This is the real cause of many of the accidents that befall inexperienced aviators, when out flying, perhaps by themselves. The night, of course, was far spent. The fog was lightening imperceptibly. Their watches betokened that it was nearing three a.m. Blaine got out his megaphone, for talking at high altitudes is much a matter of expanded lung power. He began, as usual, with a joke. "Like to 'a' got you back there!" he shouted. "Where you been?" "Looking for you mainly. What you going do next?" "See that line of fire off norwest! We that's where our front and Johnny Bull's join. Appincourte Bluff seems either to have been turned or to have turned Fritzy off. Ready for a scrimmage?" "You ought to know, Lafe!" Bangs laughed easily into the megaphone. "Ready for most anything." "Well, our front there is rather weak. Follow me. Don't lose me. We'll give that infantry a time trying to find out who we are that's spitting on them from overhead. Catch me?" "Yep-fire away! Suits me!"