Heroes and villains alike use airplanes instead of horses in this generally well-made Mascot serial featuring diminutive cowboy star Bob Steele. Steele and sidekick Guinn "Big Boy" Williams (whose supposedly comical craving for jellybeans quickly becomes tiring) are hired by an aviator friend (Jack Mulhall) to aid Lafe McKee and his daughter Lucille Browne in safeguarding the building of a dam. A mystery villain known only as "The Black Ace" is using a gang of air pirates in a (largely unexplained) war against the construction firm. The mystery villain proves, of course, to be the one character seemingly above suspicion. In fairness to the serial, we shall refrain from divulging his identity, however. Mystery Squadron contains many well-made aerial fights and stunts but is also filled with all kinds of silly and seemingly unnecessary gaffes. When a dart carrying a warning note is thrown through a window, for example, that same window is shown in the following shot as not only securely closed but covered by an undamaged lace curtain.