Set in New Orleans and the Bayou country of Louisiana during the period of the War of 1812, it is the story of fourteen-year-old Ned Greentree, who arrives in New Orleans after a long trip down the Mississippi from a Kentucky farm, hoping to find his uncle Charlie who had left home some years before. Soon he meets and joins Jean Laffite and his band. He serves Laffite as clerk and as a sort of companion-bodyguard for a Spanish boy of his own age who lives with the band but is not trusted by Laffite.

Ned spies for Laffite, who is a loyal American and supports his adopted country in spite of the poor treatment he and his band receive at the hands of the local government. With Ned's help, a cache of badly needed munitions is turned over to General Jackson, though Jaime, the Spanish boy, and other disloyal members of the band had plotted to give them to the British.

The climax of the story is the historic Battle of New Orleans, in which Ned plays an active part, and which is victorious for the American army largely because of Laffite's cooperation with General Jackson.