Natalie's family pushes her into marrying her stepsister's cast-off groom, a supposed disgrace. He's secretly a billionaire heir.
Everything rides on one delayed reveal. Natalie marries "down," the husband's wealth stays concealed, and the payoff is the reveal scene plus the family's reversal — the billionaire genre's most-worn shape, worn for a reason. The substitute-bride opening supplies the in-law antagonists the genre runs on.