In Texas, in 1941, a rainstorm washes out a train trestle, stranding passenger Lucy Gallant at the New City depot. Lucy is befriended by the manly Casey Cole, one the few ranchers left in the oil-mad boom town, who drives her in his truck to the local hotel. Lucy, who is on her way to Mexico from New York, is polite but reserved with Casey, despite his obvious interest in her. When she learns that the hotel is booked up with noisy, drunken men, Lucy tries to rest in the lobby, but is pestered by the newly rich Harry Wilson. Casey comes to Lucy's rescue and takes her and her many suitcases to Molly Basserman's boardinghouse. There, Casey insists that Lucy stay in the room he sleeps in when in town, and Molly immediately deduces that Casey is attracted to the sophisticated Easterner. The next morning, Molly introduces Lucy to her neighbors, who are awed by Lucy's Parisian clothes and accessories.
While strolling through New City, Lucy becomes the object of much attention, as the local women marvel at her stylish attire. Seeing an empty, makeshift storefront operated by a black man named Summertime, Lucy gets an idea and, before long, is selling the contents of her luggage to the fashion-hungry women of New City. By the end of the day, Lucy has made $4,800 and tells Casey that she has decided to remain in New City and open a clothing shop. Although pleased that Lucy is staying, Casey expresses doubt about her ability to secure a loan from banker Charlie Madden and run a business.
Ignoring Casey's skepticism, Lucy, who has admitted that she sold off her trousseau, persuades Charlie to lend her the money, then announces that she is going to install her shop at the The Red Derrick, a brothel. Lucy quickly negotiates a deal with The Red Derrick's owner, Lady "Mac" MacBeth, and the conversion begins. Soon after, Lucy is preparing for the opening of Gallant's, Inc. dress shop when Casey stops by to invite her to lunch at his ranch. Though at first hesitant, Lucy enjoys her afternoon with Casey, who explains that he is waiting to sell his land to the oil companies until the neighboring land has been determined to be oil-rich. With Summertime's help, Gallant's proves a success, and Lucy repays Charlie.
Later, Lucy visits Casey at the ranch to ask him to a party that Molly and her husband Gus, who have recently struck oil, are giving and proudly tells him about her financial success. Commenting that they were destined to be together, Casey asks Lucy to marry him, but intimates that he wants her to give up her store. In response, Lucy reveals that her former fiancé left her at the altar after her businessman father was indicted for fraud and committed suicide. After Casey accuses her of "building a fence around her" and ridicules her for wanting to prove herself, Lucy leaves in a huff. Lucy and Casey remain friendly but distant, and Casey enlists in the Army after the bombing of Pearl Harbor.
During the war, Lucy sends Casey letters and packages, and while recuperating from a war injury, Casey decides to go into business with Harry and Gus. One night, after the war, Casey returns quietly to New City and shows up unannounced at a party at Gus and Molly's palatial new home. Casey is cautious and sarcastic with Lucy, and she leaves, angry. Urged by Molly, Casey follows Lucy home, and the two fall into each other's arms. After a passionate kiss, Casey and Lucy discuss their future together, and Lucy disappoints Casey when she reveals that she wants to build another, bigger store with a penthouse apartment. When Casey issues Lucy an ultimatum, saying that he will marry her only if she becomes a full-time housewife, Lucy refuses. Later, however, Molly convinces the heartbroken Lucy to choose marriage over career, and Lucy drives to Casey's drilling site, on which he has just struck oil. Believing that Lucy has come to ask for money, Casey is rude, and Lucy departs without admitting her feelings.
In town, she then discovers that her store has burnt to the ground. Feeling that her new store idea is too risky, Charlie turns down Lucy's next loan application, but privately, the now-wealthy Casey pressures the banker to change his mind. While Gallant's, Inc. is being rebuilt, Casey leaves on an extended European vacation and becomes engaged to a Parisian model, news of which is published in the New City papers. The engagement falls apart, however, and Casey flies back to New City on the eve of Gallant's first anniversary celebration. Mac, who once had a fling with Casey, meets him at the airport and takes him to another posh party at Gus and Molly's.
Casey is disappointed to see Lucy with Jim Wardman, Gallant's suave general manager, and acts unimpressed when Lucy announces that the governor is coming to the store's anniversary celebration. Just before the governor's arrival, Lucy meets with her board, on which Charlie and Mac serve, and is thunderstruck to learn that Charlie's $250,000 note is due and unpayable. Although Jim insists that he warned Lucy about the store's precarious finances, Lucy and Mac know that he manipulated her in order to take over the business, but are powerless to stop him.
Lucy presents a brave front during the governor's speech and a fashion show featuring original Gallant's creations, and when Casey appears and learns about her troubles from Charlie, he offers to pay the note so she can save the store. After Charlie finally tells Lucy about both times Casey interfered on her behalf, Lucy runs to Casey and declares she wants to marry him, with no store attached.