In the 1890s, Sgt. Major John Philip Sousa, leader of the Marine Corps Band, meets Private Willie Little, inventor of an instrument he calls the Sousaphone...and Little's girlfriend, shapely showgirl Lily. To support his growing family, Sousa leaves the Marines and forms his own band; Willie and Lily go along. Though he'd rather write ballads, Sousa's marches bring him increasing fame; from their debut in 1892 the band is a great success. But Sousa's 'no wives' rule threatens the romance of Willie and Lily...as does the Spanish-American War.