Maisie Ravier (Ann Sothern) loses her job as an assistant in Horatio Curley's dog act as a result of a minor quarrel with test pilot "Breezy" McLaughlin (James Craig). Breezy gets Curley a job at the Victory Aircraft factory where he works and offers to use his influence on Maisie's behalf too. However, she insists she can get a job there on her own merits. She lands on the swing shift at the factory. Breezy does, however, get her a room at the boarding house owned by Maw Lustvogel (Connie Gilchrist). Despite her initial dislike for him, Maisie starts falling in love.
Maisie stops a suicide attempt by failed actress Iris Reed (Jean Rogers), who lives across the hall, and persuades her to get a job in the same place. Her kindness backfires on her when Breezy is more attracted to Iris. The two soon become engaged.
When Breezy gets his wish to join the United States Army Air Forces, he asks Maisie to look after Iris while he is away being trained. Maisie finds this a difficult task, as Iris turns out to like men altogether too much. When Iris gets fired, she uses her feminine charms to get Judd Evans, a factory clerk, to pay the rent for an apartment in his building. She skips out without paying Maw the back rent she owes, even though Maisie gives her $20 to do so, and she has just received a $100 money order from Breezy.
Maisie finds Judd comforting Iris after another "suicide attempt". She orders Iris to tell Breezy that she no longer loves him when he comes home on leave to marry her. However, Iris secretly accuses Maisie of suspicious behavior to the factory's security department. While Maisie is being questioned, Iris and Breezy drive to Yuma, Arizona to get married. Maisie cleverly confesses to being a saboteur and implicates Iris and Breezy as fellow agents. They are stopped by the police, but let go after Breezy produces his identification. However, Breezy learns that Maisie is being held, even though Iris told him that she left to attend the funeral of an aunt. Having learned of Iris's shady character, Breezy goes back to Maisie. She is initially unwilling to take him back, but eventually gives in.
In Swing Shift Maisie, Ann Sothern was reprising a familiar role as the "gum-cracking, back-talking Brooklyn bombshell". MGM studio bosses knew, however, that the series was a profitable and popular franchise.
Unlike aircraft factory settings for other wartime films such as Captains of the Clouds (1942) that used the Lockheed Vega Burbank factory, Swing Shift Maisie was set in a fictitious "Victory Aircraft". MGM studios had bought two Lockheed P-38 Lightning fighter aircraft for a film project on the air war in North Africa, simply titled "P-38". The project was never realized but one of the aircraft was featured in A Guy Named Joe (1943). The other P-38 appears in the factory scene in Swing Shift Maisie.
Swing Shift Maisie, filmed at Grand Central Air Terminal, Glendale (Los Angeles), also used a Northrop A-17A, Seversky SEV-3 and Douglas DC-3 in some scenes.
Film critic Theoore Strauss in his review for The New York Times, thought Swing Shift Maisie had become stale, but still saw the charms of the main character. "She is still the hapless little Miss Fixit all too often hurt by the people she helps, the good fairy from the honky tonks who behaves as if the world were filled with nothing but the nicest people. Her taste is not precisely refined. It runs to furbelows, bric-a-brac and ugly little dogs. Her conversation is not always as elegant as it aspires to be. But Maisie has a very strict credo even if it never got beyond the grammar-school stage. Above all she has a heart. Maisie isn't synthetic, but her latest adventure is."