The third volume was "The Boy Scouts and the Army Airship," referred to in connection with Lieutenant Duvall. In this book a military biplane played an important part, as did the theft of a series of plans of a gyroscope invention of Lieutenant Duvall's, who was an all-around mechanical genius. In the story that preceded the present account of the Eagle Patrol the lads found themselves in the Adirondacks on a strange mission. With a certain Major Dangerfield, a retired army officer, they searched for a lost cave in which an old-time pirate, one of the Major's ancestors, had hidden his loot when Indians threatened him. How the cave was located and the startling discovery made there, we have not space to describe here. But in the wildest part of the "land of woods and lakes" the boys encountered some thrilling adventures, not the least of which was Rob's battle with the moonshining gang that infested a lonely canyon. From this trip they had returned not more than two weeks before the scene in the meeting-room, which we have described, took place. Bronzed, clear-eyed and alert, they were already longing for action of some sort. How soon they were to be plunged into adventures of a variety even more exciting than any they had yet encountered they little dreamed at the moment. - - - - - They were still laughing over the idea of the substantial Tubby's rotund form being compared to a shadow when there came a tap at the door of the room in which they were assembled. "Guess that's Andy Bowles," said Rob, referring to the only member of the Patrol who was not present; "wonder why he's so late." Then, in a louder voice, he cried: "Come in, Andy." But the voice that answered as the door was flung open was not Andy's. Instead, it was a deep, resounding bass one. "I'm not Andy; but I'll accept the invitation." As the owner of the voice, a tall, well-set-up man with a military bearing, stepped into the room all the Scouts sprang erect at attention, and gave the Scout salute. Then they broke into three cheers. "Why, Lieutenant Duvall, what are you doing here?" exclaimed Rob, coming forward. The young officer shook hands warmly with the leader of the Boy Scouts. Then, while the others pressed closer to the lieutenant--the same officer who had conducted the aviation tests at the "tunnelled house"--he addressed Rob. "The fact is, I came down here to see if you are willing to tackle some more adventures," he said. "Are we--" began Rob; but a roar from the Scouts interrupted him. "Just you try us, Lieutenant." "More adventures? Great stuff!" "I'm ready right now." "You can count on me." The air fairly bubbled with confusion and excitement. The Lieutenant roared with laughter. "I do believe if you boys were told to lead a forlorn hope up to a row of machine guns you'd do it," he exclaimed; "but all this time I've been leaving my friend outside. May I bring him in?"