Finian, a whimsical and optimistic Irishman, arrives in the fictional Southern state of Rainbow Valley with his daughter Sharon and a stolen pot of gold. He hopes to bury the pot near Fort Knox, believing this will cause it to multiply. The town is populated by poor but welcoming sharecroppers who are struggling to keep their land from being seized by the racist Senator Billboard Rawkins. As Finian and Sharon adapt to their new surroundings, their presence starts to bring unexpected changes to the community, both magical and social.

Sharon falls in love with Woody Mahoney, a local farmer and activist who dreams of better prospects for his people. Meanwhile, Og—the leprechaun from whom Finian stole the pot of gold—appears, desperate to retrieve it before he loses all his magical powers. Confusion and chaos ensue as the pot of gold grants wishes with unforeseen consequences, complicating relationships and challenging the status quo in Rainbow Valley. The magical events set off by Finian's schemes lead to a series of adventures that influence the lives of every townsfolk, culminating in a pivotal confrontation that addresses issues of greed, prejudice, and transformation.