The Firefly (1937)

Nina Maria Azara is a captivating singing spy for Spain during the Napoleonic Wars, tasked with seducing French officers to gain information about Napoleon's plans for Spain. She is sent to Bayonne, France for her mission and meets Don Diego at a club before leaving for France. Unbeknownst to Nina, Don Diego is actually Captain Andre, who was sent to spy on her. After falling in love with Diego, she learns of his true identity. Nina escapes her captors and returns to Spain, but goes into hiding when Napoleon's troops invade the country. Nina and Captain Andre are surprisingly reunited but now find themselves on opposing sides of the war.