On a scientific expedition to Siam young Billy Batson is given the ability to change himself into the super-powered Captain Marvel by the wizard Shazam, who tells him his powers will last only as long as the Golden Scorpion idol is threatened. Finding the idol, the scientists realize it could be the most powerful weapon in the world and remove the lenses that energize it, distributing them among themselves so that no one would be able to use the idol by himself. Back in the US, Billy Batson, as Captain Marvel, wages a battle against an evil, hooded figure, the Scorpion, who hopes to accumulate all five lenses, thereby gaining control of the super-powerful weapon.

Dr. Cross, a psychiatrist, is treating a young woman, Janet Stewart, who is in a coma-state, brought on when she heard loud arguing, went to her window and saw a man strike his wife with a candlestick and kill her. As she comes out of her shock, she recognizes Dr. Cross as the killer. He takes her to his sanitarium and urged by his nurse/lover, Elaine Jordan, gives Janet an overdose of insulin. But he can't bring himself to murder her in cold blood and asks Elaine to get the medicine to save her. She refuses, they argue, and he strangles her. He saves Janet's life, but now faces two murder charges.

After Confederate officer Blayde Hollister's home and family are destroyed by the Marlowe Brothers during the Civil War, he swears revenge, refusing to surrender and becoming a wanted man. In order to pursue the three brothers into Texas, Hollister fakes his own death in a staged gunfight with his friend Wild Bill Hickock. He then befriends Martin Weatherby, the newly appointed U.S. Marshal to Dallas, an affable, but not very experienced lawman, who agrees to let Hollister assume his identity. The eldest of the Marlowe brothers, Will, masquerades as a law-abiding real estate dealer while feigning righteous indignation over the brutal acts of lawlessness and violence visited on the honest citizens of Dallas by his sociopathic brothers, Cullen and Bryant. (Their parents were evidently fond of the renowned poet William Cullen Bryant). When Hollister becomes a rival for the affections of Weatherby's aristocratic fiancee Tonia Robles, Martin wonders whether he should let Blayde know that ...