Henny, talent scout for the Margaret Ames Film Agency in Hollywood, mistakes Judy and Marian, the understudies, for Eileen and Betty, the real stars of a Broadway show and signs them up for movies. Margaret, furious with Henny for the blunder, fires him---but only temporarily. Another agent, Marty Allen, once married to and still in love with Margaret, signs Betty and Eileen. Henny arrives with Judy and Marian, and the nightclub manager asks Henny to emcee the show. Though he is not sure himself what they can do, Henny introduces the girls and they make a hit in a dramatic sketch. (Simmer down, it's just a Monogram movie, and their nightclub attendees can react anyway director Phil Karlstein/Karlson wants them to.) Big-time movie producer R. J. signs them to a film contract. So, what does this have to do with the title, "A WAVE, a WAC and a Marine"? Because Judy joins the WAVES, Marian the WACS and Marty the Marines and all have two weeks before induction, and that is more than long enough to shoot a Monogram musical-within-a-Monogram musical and have a few days to spare.