After his father was killed trying to alert the authorities to a conspiracy of crooks and politicians, Bill Waring travels the world to learn all fighting forms and weapons. He returns as the Challenger, challenging everyone connected to his father's death.; Lt. Peter Noble is the sole survivor of a wrecked U.S. Navy submarine. As he escapes the wreck he finds himself unable to float and ends up inside a cavern populated by flying mer-men. After he defeats their leader they hail him as the reincarnation of their hero, the Fin, so he puts together a costume to fit the name.; Professor Elton Morrow finds an enormous blue diamond on an Antarctic expedition, but it is shattered when Nazis attach his returning ship and the fragments become embedded in his body. Discovering that his whole body has become as hard as a diamond, he thwarts a burglary at his museum and decides to created a costumed identity for fighting crime.; Jerry Carstairs uses his radio skills to intercept Nazi messages and construct the booming voice he uses as the Thunderer. While discouraging his friend Eileen from reporting on the fifth columnists for her own safety by day, by night he protects her and fights against the Nazis as the Thunderer.; In the far future, Captain Daring and Susan Parker lead the forces of the U.S.A. against attackers from an underground city.; Mr. Million helps a boy who his trying to pay for his sick mother's medicine, but has to do it indirectly as the boy refuses any money he hasn't worked for.; Betty Barstow, secretary for private detective Dan Hurley, dresses in a costume to go to a masquerade but ends up foiling a crime at the cemetery with her jiujitsu skills instead.; Officer O'Krime can't figure out whom to protect and whom to arrest.