The Eagle uses sky writing to make threats against a corporation. Nathan Gregory owns a traveling fairground and is thought to be the Eagle. Craig McCoy is a pilot who goes looking for the Eagle when Gregory turns up missing.
The period is the 1820's and the first wagon train leaves Independence heading west to Santa Fe. In order to maintain his power, the ruthless Official at Santa Fe must not let them arrive and he sends out his men to stop them. The wagon train then has to endure repeated attacks but is aided by a mysterious rider that shoots singing arrows and rides a painted stallion.
Secret Service Major Steel (Joseph W. Girard), is one of the few men in America aware of the fact that Captain Albright (Dave O'Brien) is also Captain Midnight, daring masked aviator dedicated to fighting gangsters and enemies of America. When murderous bombing attacks are made on West Coast munitions plants, Steel sends for Albright and asks him to track down the mysterious Ivan Shark (James Craven), the foreign agent mastermind behind the attacks. Shark has learned about an ingenious range finder, invented by John Edwards (Bryant Washburn, and makes plans to obtain a model of the invention. Edwards instructs his daughter, Joyce (Dorothy Short), to bring the model to Albright for safekeeping in his mountain laboratory. Shark takes Edwards prisoner by Albright assures Joyce that her father will be saved and an end put to Shark's reign of terror. Dressing as Captain Midnight and enlisting the aid of his friends, Chuck (Sam Edwards) and Ichabod Mudd (Guy Wilkerson), Captain Midnight delivers on his promises fourteen chapters later.