 Chapter 1, "The Black Ace" opens with dam-project foreman Hank Davis (Jack Mulhall) hiring two stunt flyers he once flew with, Fred Cromell (Bob Steele) and Bill "Jellybean" Cook (Guinn Williams), to protect the dam from the air raids by a group known as the Mystery Squadron, under the leadership of the mysterious Black Ace. Each attack is preceded by the arrival of a miniature airplane carrying a warning that the Mystery Squadron is about to attack. This makes the workers somewhat disturbed and distressed to the point that they mistake Fred and Bill for members of the criminal air armada. The workers form a vigilante lynch mob from which Fred and Bill must escape and continue their 12-chapter search to unmask The Black Ace. Those in a hurry can flash-forward to the ending of chapters 4-6-8 and 12, as they are all "cheater chapters" comprised primarily of various players recapping, via flashback footage, what has transpired in preceding chapters.Mascot and Republic led the serial world in the use of cheater chapters, but they usually only had two, so "The Mystery Squadron" with four may hold the record for short-changing tatics.