In 1931, Elizabeth Rambeau comes from England to live in California with her aunt and uncle of a winemaking dynasty, who are still wealthy despite 12 years of Prohibition. Object: marriage to the heir of another vineyard, to further consolidate holdings in the Valley. But John Rambeau, Elizabeth's illegitimate cousin, has other ideas about who she should marry, and sharply opposes patriarch Philippe's refusal to sell wine grapes to bootleggers. John's activities bring violence to the valley, and soap opera to the Rambeau family...

In the 1930s, Londoner Elizabeth Rambeau tries to hide her disappointment when her father Lon sends her to Napa Valley to live with his father Philippe and sister Martha Fairon. The first night that she arrives at the family's vast vineyards and grand estate, Philippe and Martha welcome her with a lavish party, at which Philippe delivers his customary speech declaring the grape proof of God's existence. He then announces the upcoming marriage, heretofore unknown to Elizabeth, between her and her cousin, Andre Swann. Later, to Martha's displeasure, another Rambeau cousin, John, pursues Elizabeth and leads her into the vineyards. Mischievously hoping to shock her, John enlightens her about the Rambeau family: Philippe married his daughters, Martha and John's mother Charlotte, to other local landowners in order to increase the vineyard holdings, and presently runs the estate with Martha. He now wants to marry Elizabeth to Andre in order to absorb Andre's Stag's Leap winery. Andre wants to be a priest, but was not allowed to leave the family business. John then points to his house nearby, in which Charlotte is invalided, and explains that he knows that Martha's husband Francis is his real father, even though everyone claims that Charlotte's late husband sired both him and his sister Monica. John then takes the speechless Elizabeth into his arms and kisses her, declaring that she is not as innocent as she appears, but she pulls away and runs into the house. The next day, John arrives for a wine tasting and, after demonstrating his perfect understanding of wines and desire for bold changes, insults Philippe by insisting that they ignore Prohibition laws and sell their grapes to bootleggers. Philippe, who loves John but adamantly insists on remaining lawful, explains once again how he will continue to cultivate and study wines until he can legally sell them. John then volunteers to show Elizabeth around the winery, bitterly pointing out the vast stores of wine going to waste. When he suddenly asks her about her past and tries to kiss her, she once again pulls away. John leads her outside, where one of the female workers, Buz Dietrick, throws a grape at him flirtatiously to gain his attention. Martha spirits Elizabeth away to lunch with Andre, who avers his belief that arranged marriages can be very "serene." Soon after, John assembles the grape grower's association members and announces that he can secure huge profits if they sell to a syndicate in Chicago. Some of the growers, many of them recent immigrants, insist on gaining Philippe's approval, although John warns them that they must all band together to wield economic power. Days later, John leaves for Chicago, after which syndicate thugs visit the reluctant growers and, through violence and threats, force everyone to sign the contract. By the time John returns months later, the growers, grown rich from his dealings, welcome him warmly. He joins them at a nightclub, where Buz sits with her boyfriend, Luigi Griffanti, and Elizabeth dances with Andre. Monica introduces John to her new fiancé, Nate Forster, whom John accepts regardless of his Jewish background. John then invites Elizabeth to dance and confesses that he is desperately in love with her. Attracted to him but hoping to dissuade his interest, Elizabeth reveals that her father sent her away from England because she was embroiled in a torrid affair with a cruel man, and she now desires a safe marriage to Andre. Jealous, John accuses her of "prostituting" herself for Stag's Leap, and she slaps him. John then turns to Buz for comfort, convincing her to leave Luigi and drive off with him. Later, Andre drives Elizabeth home, where he confesses that he is growing to love her. Inside, Martha, who has seen Elizabeth conversing with John, confronts her about her past, urging her to marry Andre before he realizes he is getting "damaged goods." Meanwhile, John returns home and tells his mother he will leave the next day for Chicago. Although Charlotte worries that he will remain lonely and bitter, the next day Elizabeth races to meet John's train before it departs, and affirms her love for him. Thrilled, John insists that she wait for his return. A few months later, a pregnant Buz claims the baby is John's, and with her father blackmails Philippe to remain quiet. When Elizabeth hears, she collapses with grief, but Martha shrewdly directs Buz to tell Luigi the baby is his. Buz and Luigi soon marry, but she fights with him and his mother when they want to name the baby Cesare instead of John. As the months pass, Charlotte and Philippe spend time together, while Martha tries to convince Andre to wait for Elizabeth, who refuses to set a wedding date. When John finally returns to Napa Valley, Elizabeth is in the mountain orchard with Philippe, who explains that this is sacred ground to him, as it was his first plot of land and his beloved wife is buried here. At the estate, Martha greets John coldly and warns him that he must conduct business through her, because Philippe is ill. After persuading her that they can make millions by selling the Rambeau grapes to the syndicate, John drives to the orchard. There, Philippe, who is horrified by John's shady dealings, commands him to leave, after which Elizabeth spurns him for fathering Buz's baby. Protesting that he can prove that Buz lied, John races away, accidentally throwing a lit cigarette into the parched fields, where it starts a blaze. By the time Philippe spots the fire, it is out of control, and destroys most of the orchard. Meanwhile, John rushes to Buz's house, where Mrs. Griffanti, upon noting his first name, assumes the worst. Just as Buz agrees to tell Elizabeth that the baby is not John's, Luigi, at his mother's urging, falls on John in a jealous rage. John manages to get away, but Luigi retrieves a gun and shoots him. John is diagnosed with partial, possibly temporary paralysis, and when Elizabeth visits the hospital to beg his forgiveness, he turns away from her bitterly. Soon, he is able to walk with crutches, and returns home, where he confronts Francis and Charlotte with the truth about his parentage and admits to starting the orchard fire, forgiving them and asking for the same in exchange. Months later, after Philippe's death, Martha gathers the family for the reading of the will. To her shock and dismay, Philippe has divided the estate equally between his children and grandchildren, and left the orchard to John and the valley vineyards to Elizabeth. Although Martha is greatly pained by what she sees as an injustice, Francis realizes that now she will finally turn to him instead of work, and they embrace. Within weeks, John has restored the scorched orchard to health. One day, Elizabeth joins him with a valley grape vine cutting to add to his, to "blend the softness of the valley with the strength of the mountain." They plant together in silence, finally falling into each other's arms.