Mirror magazine's top photographer Katherine Grant (
Claudette Colbert) is assigned to photograph the Interborough Vehicular River Tunnel project in New York City. Wearing a hardhat and boots, the beautiful photographer is taken underground to the construction site where she is
not greeted warmly by the superstitious tunnel workers, called "sandhogs", who believe that women in the tunnel bring bad luck. When she sneaks closer to the drilling point to get a better view, her presence distracts some of the workers and causes an accident that nearly kills Jim Ryan (
Fred MacMurray), the cocky well-built sandhog they call "Superman". When she sees the unconscious Ryan about to be crushed by a machine, she drags him to safety. Later in the compression chamber, a revived Ryan gets into a fistfight with his co-workers after they taunt him about being saved by a woman. During the brawl, Katherine photographs Ryan as he's beating up the other sandhogs. On their way out of the tunnel, Ryan notices that Katherine is flirting with him and tells her he's not interested. Insulted by the brush off, she informs him that she has a boudoir chair with more integrity than he has. Back at home, Katherine shows her photographs to her sister Hoppy (
Ilka Chase) and their snobbish sophisticated friends—her effete suitor and
Mirror publisher Henry Fulton (Paul McGrath), playwright Dunbar (Morton Lowry), and composer Roger Winant (
Richard Haydn)—who make fun of the brawling "ape". Just then, Ryan arrives at Katherine's apartment to return the tripod she left behind and demands to see the "chaiah" that has more integrity than he does. Unimpressed, Ryan kisses a flustered Katherine flush on the lips and then dismisses her, having regained his confidence. Before he leaves, Ryan is approached by Henry and Dunbar who demand that he provide details of his heroic fistfight; picking up on their condescension, Ryan reenacts the fight, roughing them up in the process. In the coming weeks, Katherine is haunted by pleasant dreams of Ryan as a superhero rescuing her from Henry as an evil assailant. Meanwhile, Ryan loses his job after Henry publishes the photograph of the sandhogs fighting. When Ryan shows up at her apartment, Katherine assures him she did not know the photo would be published, and offers him a job as her assistant to offset his lost wages. Thinking that if she spends time with him, she will prove to herself that he is not worthy of her. They go on several assignments together, and despite his flirtations with various cheap blondes, Katherine eventually falls in love with Ryan who returns her feelings. One night after sharing a passionate kiss, they are spotted by Hoppy who reveals Katherine's original plan to get him off her mind. Feeling that he's been used, Ryan walks away disgusted. Sometime later, the tunnel project is threatened by repeated cave-ins resulting from the constant flow of "muck" coming in from the riverbed. The project's one hope at stabilizing the muck is a new machine and chemical process invented by Ryan—an engineer—who was working as a sandhog to better understand the problems of underwater construction. Assigned to cover the testing of this new machine, Katherine returns to the tunnel and is shocked to learn that the inventor is Ryan. She sneaks into the testing area and finds a good vantage point, while Ryan and the sandhogs start up the machine and remove some planks holding back the muck. At first the test appears to fail, but as Katherine takes several photographs, the chemical reaction begins to solidify the muck. Just then a breach of the upper wall creates a muck-slide that nearly buries Katherine. Ryan and the others abandon the machine to save her. Afterwards, the officials declare Ryan's test a failure. After everyone leaves, Katherine convinces Roger and one of the sandhogs to accompany her back into the tunnel to retrieve the camera, which she believes can prove that the machine was working. They find the camera and indeed the photos show that the muck flow was stopping when the breach occurred. When she shows her proof to the city officials, they agree to move forward with the project under Ryan's leadership, accepting Katherine's condition that Ryan never know that she was responsible for the decision. Believing that Ryan will never forgive her for all the trouble she's caused, she accepts Henry's marriage proposal. Knowing that Katherine is still in love with Ryan, Roger visits him at his office and reveals her plan to marry Henry, despite her true feelings for Ryan. Darlene, one of Ryan's showgirl acquaintances overhears and goes to Katherine's apartment, barges into her engagement party, and warns her to stay away from Ryan. When she slaps her, Katherine responds by knocking her off her feet with one punch just as Ryan arrives. Ryan takes Katherine and Henry into her bedroom. Holding up Henry with one hand and the "chair" with the other, he asks her to choose. When she chooses Ryan, he picks her up, throws her over his shoulder, and proudly walks off to get married. ==Cast==