This is a somewhat long and unsatisfying lensing of the 1912 Rudolf Friml operetta, which starred Emma Trentini and Henry Vogel on Broadway. Jeannette MacDonald stars here as Nina Maria, aka the "Mosca del Fuego" (Firefly), a singer in a Madrid cafe in 1808. Singing is only her cover job,
however; she is actually a secret agent working for the Marquis DeMelito (Douglass Dumbrille), an advisor to King Ferdinand. Napoleon is planning to invade Spain, and Nina Maria must discover his plans. She becomes friendly with Col. DeRougemont (Warren William), one of Napoleon's confidantes,
tries to enlist Diego Manrique de Lara (Allan Jones) in her cause before learning he is ...