Police Lieutenant Dan Barton, ordered to contact and smash a mysterious Axis sabotage ring, arranging to have himself thrown off the police force in disgrace.
He calls attention to himself by assaulting a high government official, the custodian of a newly-devised formula for the manufacture of synthetic rubber, in a faked "effort" to steal the formula.
While under the "protection" of the saboteurs who are still suspicious of him, Dan learns that they have been ordered to capture the secret formula by a secret code, whose method of operation is in itself of vital military value.
Escaping and disguising himself in a specially-made "Black Commando" suit of fire-proof material (with no Super-Hero powers beyond those possessed by his stunt double), he foils the first Nazi attempt.
From that moment on, Barton plays a risky game of life and death; as a disgraced policeman, he becomes an accepted member of the gang and as the Black Commando, he fights them at every turn.
And, in either role, he is a hunted fugitive, sought by both the Police and the Federal Government.
With the aid and assistance of reporter Jean Ashley and his police partner, Pat Flannagan, Barton manages to round up the ring, locate its secret code and destroy the most serious sabotage effort ever planned by Hitler agents in America.
Plus, at the end of every chapter, a series of lessons on code, written and directed by code expert Henry Lysing, was given, and a book called "The Secret C O D E Digest" (by Mr. Lysing) was on sale in the lobby for ten cents