International Lady(1941)

Overview:

Tim Hanley, an American agent, posing as a lawyer with the United States Embassy in London, and Reggie Oliver, a Scotland Yard detective, posing as a music critic are both keeping their eye on Carla Nillson, a famous singer, whom they suspect of espionage. They all meet in London, then in Lisbon, and eventually in New York City, where Carla sings on the radio.