They had been spending all their spare time, when not in school, working upon the line that seemed to have a strange fascination for them.  Frank’s father was one of the best known doctors in town, a man of considerable means, and with a firm faith in his boys, so that he was easily convinced whenever Frank wished to do anything.

Andy had been living with his guardian for some time, until the return of his own father, Professor Bird, who had been lost while attempting a difficult balloon trip in Central America, and found in a most miraculous way by the two boys as told in a previous story.

Andy had inherited the passion which his father, a noted professor, had always had for navigating the air.  It was a favorite expression of his “A bird by any other name would fly as high,” and his cousin would retort:  “A Bird takes to the air just as naturally as a duck does to water.”

They had been doing some fine “stunts” during the last year or two; and it may be supposed that the people of Bloomsbury were more than a little proud of seeing the name of their town mentioned so favorably in the papers in connection with the doings of the Bird boys.

Of course, as is always the case, there was a rival in the field, who had been the cause of much trouble in the past, and still watched their work with an envious eye.  This was a boy by the name of Percy Shelley Carberry, rather a bold fellow too, and as smart as they make them, only unscrupulous as to the means he employed by which to gain his ends.

Percy was the only son of a rich widow, who could never refuse him anything he demanded; and with unlimited cash at his disposal he had been able to do quite a few feats himself that might have gained him more or less fame, only that they were eclipsed by the accomplishments of Frank and Andy; and that was where the shoe pinched with Percy.

His temper was one of his weak spots, also a liking for fast life, which, of course included tippling; and the aviator who indulges to the slightest degree in strong drink is next door to a fool; for as he takes his life in his hands every time he leaves the ground, the necessity for a clear brain is apparent.

In most of his tricky work young Carberry had for a boon companion one “Sandy” Hollingshead, a sinewy chap, whose most prominent trait was his faculty for disappearing suddenly in a pinch.  He was considerable of a boaster, but could always invent a most remarkable excuse for going before the storm broke.  But Percy, no coward himself, knew how to make use of his sly crony; and despite their numerous quarrels, that often ended in actual fights, the pair of precious tricksters still kept company together.

Sandy was freckled had pale eyes and very blonde hair, that gave him a queer look.  Those eyes never could look any one straight in the face, but shifted uneasily; and other boys said that Sandy, the cigarette smoker, was always on the watch for a quick “getaway.”