Henny (Henny Youngman), talent scout for the Margaret Ames (Sally Eilers) Film Agency in Hollywood, mistakes Judy (Anne Gillis) and Marian (Elyse Knox), the understudies, for Eileen (Marjorie Woodworth) and Betty (Ramsay Ames), 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 (Richard Lane), 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. (Alan Dinehart) 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.
Henny Brown, a talent agent for the Margaret Ames Film Agency of Hollywood, is sent East to sign Eileen Manners and Betty Mitchell, the stars of a Broadway show, to a movie contract. Mistaking their understudies, Judy Blake and Marian Jessum, for the stars, Henny offers them a contract and escorts them back to Hollywood, where his employer, Margaret "Maggie" Ames, fires him for his blunder. After Henny's dismissal, agent Marty Allen, who has signed Eileen and Betty to a contract, offers his clients' services to Margaret. Marty, who was once married to Margaret and is still in love with her, arranges for them to celebrate the occasion at a nightclub that night. Mellowed by her ex-husband's attention, Maggie relents and rehires Henny. When she informs him that Mike Carter, the owner of the club, needs an act for that evening, Henny offers to emcee the show for free in exchange for the opportunity to showcase Judy and Marian. Although he is unsure of their abilities as serious actresses, Henny introduces Judy and Marian as promising new entertainers, and they create a sensation with their dramatic performance of a skit. Impressed, the famous producer R. J. signs them to a contract and forecasts a brilliant career for them. This infuriates Eileen and Betty, who are also under contract to R. J. and demand to star in his next film. Marian's joy is short-lived, however, for she soon receives a cable from the War Department notifying her that her husband Bill has died in battle. Grief stricken, Marian and Judy enlist in the Armed Forces, and Marty settles the dispute by suggesting that R. J. cast them in his current picture, as they are scheduled for induction in two weeks. Maggie then placates the indignant Eileen and Betty by offering them roles in R. J.'s film. All ends happily as the cameras begin to roll, and Margaret, impressed by Marty's ingenuity, develops a new appreciation for her ex-husband.
