Tom Wayne rescues Clancy, Renard and Schmidt in the Arabian desert and they join him in going after El Shaitan, a bad guy who is never seen as he tries to wipe out the Foreign Legion.
Beyond Hell's Gate Pass is territory controlled by a man who calls himself King Carter; he uses a variety of schemes to prevent the railroad from being built, for fear it will finish his control of (what he considers) his land.
Hank Davis, foreman on a huge dam project, enlists the aid of his two flyer friends when a sinister figure known as The Black Ace leads his Mystery Squadron of masked pilots in an attempt to destroy the dam.
This 13 chapter serial is based on the comic strip character Ace Drummond created by Eddie Rickenbacker. Ace is a 'G-Man of the sky' working out of Washington D.C. He is sent to Mongolia to find out why a mysterious villain known only as 'The Dragon' is trying to prevent the newly formed International Airways from setting up an airport there. Ace meets Peggy Trainor (Jean Rogers) who is searching for her archaeologist father who has disappeared. Together they search for answers to the puzzles.
The struggle over the Bellamy estate ends with Michael Bellamy accused of murder and killed on the way to prison, while his brother, Abel Bellamy, takes control of the estate for his own nefarious plans.