The Mystery Squadron, a group of airborne vigilantes, begins a series of attacks on a major construction project. Their mysterious leader, known only as "The Black Ace," conceals his identity behind a mask. The project foreman hires stunt flyers Fred Cromwell and Bill Cook to deal with this aerial menace. Their mission is jeopardized when the two pilots are accused of being members of the gang. Fred and Bill must uncover the true identity of the Black Ace before they face a lynch mob themselves.