Police Lieutenant Lon McQ investigates the killing of his best friend and uncovers corrupt elements of the police department dealing in confiscated drugs.
A Major noted for advancing with his mouth before thinking is given a choice: to be drummed out of the Army, or take command of and shape up the ROTC program at Sheridan Academy before it fails its next inspection. At Sheridan he encounters three hundred pre-teen cadets who range from rascally to adorable, and a female doctor who has just the right prescription for him.
Two men with questionable pasts, Glyn McLyntock and his friend Cole, lead a wagon-train load of homesteaders from Missouri to the Oregon territory. They establish a settlement outside of Portland and as winter nears, it is necessary for McLyntock and Cole to rescue and deliver food and supplies being held in Portland by corrupt officials. On the trip back to the settlement, up river and over a mountain, Cole engineers a mutiny to divert the supplies to a gold mining camp for a handsome profit.
Mark Fallon, with partner Kansas John Polly, tries to introduce honest gambling on the riverboats. His first success makes enemies of the crooked gamblers and of fair Angelique Dureau, whose necklace he won. Later in New Orleans, Mark befriends Angelique's father, but she still affects to despise him as his gambling career brings him wealth. Duelling, tragedy, and romantic complications follow.
A scientific expedition searching for fossils along the Amazon River discover a prehistoric Gill-Man in the legendary Black Lagoon. The explorers capture the mysterious creature, but it breaks free. The Gill-Man returns to kidnap the lovely Kay, fiancée of one of the expedition, with whom it has fallen in love.