Christopher Hatton owns the country estate Mordelaine. In a tense dice game, Nick Helmar, Basil Sydney, wins and Hatton loses the estate, forcing the Hattons to relocate to a nearby cottage. One day, Barney Hatton, Dermot Walsh, witnesses villagers attacking a young woman and rescues her. She is Jassy Woodroofe, Margaret Lockwood, the daughter of Tom Woodroofe, John Laurie, and a gypsy mother. Jassy carries the gift of second sight, a trait that leads the locals to fear her as a witch.
Mrs Hatton, Nora Swinburne, hires Jassy as a domestic servant, hoping to keep the new presence quietly contained on Mordelaine. At the same time, Bob Wicks’s daughter Lindy Wicks, Esma Cannon, endures harsh treatment from her father, a situation Tom Woodroofe himself tries to intervene in.
When the Helmar family moves into Mordelaine, Nick allows Christopher Hatton to continue gambling, but the moment Hatton is caught cheating, he takes his own life. Soon after, Nick discovers his wife has been unfaithful and expels her from Mordelaine, a decision that unsettles the house as the balance of power shifts.
Tom Woodroofe leads a march of villagers to demand better pay and conditions from their landlords, and Jassy, sensing danger, pleads with Barney for help. In a drunken confrontation, Nick shoots Tom, an act that cascades through the community and the house.
Jassy and Barney grow closer, which worries Barney’s mother. Jassy is sent away to a finishing school with a strong recommendation, and she returns to Mordelaine as a maid, forming friendships with some of the young ladies, including Dilys Helmar, Patricia Roc. Dilys secretly escorts Jassy back to Mordelaine, disguising her as a school friend. Nick claims he recognizes Jassy’s surname, a reminder of the night he shot her father. Jassy reminds him that it was not intentional, and he tries to smooth things over, saying, "let bygones be bygones."
Dilys and Jassy later visit Barney, and the two women’s paths cross with Stephen Fennell, Grey Blake, as Dilys and Stephen begin an engagement that unsettles Jassy, who still loves Barney and resents Dilys’s interference.
Nick proposes marriage to Jassy, who agrees only if Mordelaine is gifted to her as part of the deal. They marry, but live separately, as their legal agreement leaves no provisions for a shared bed. In a fit of fury, Nick goes out riding and has an accident. He is brought back to Mordelaine, where a strict diet and no alcohol are prescribed, a regime Jassy enforces even as Nick's violence toward her escalates.
When Jassy visits Dilys and Stephen, Lindy decides to poison Nick by slipping rat poison into a bottle of brandy, which Nick drinks greedily. Jassy senses Nick’s death and cries out, but Stephen suspects she has killed him and has her arrested along with Lindy. At the trial, Jassy’s alibi is not enough to clear her at first, but Lindy’s sudden confession to the murder exonerates Jassy, though Lindy collapses and dies under the stress.
Barney discovers a letter in which Jassy had signed Mordelaine over to him in anticipation of her sentence. He refuses the claim on Mordelaine and realizes that his love for Jassy is as strong as his love for the estate. With the exoneration, life on Mordelaine limps toward a delicate, uncertain future, where love, loyalty, and ownership remain tangled in a web of deceit and power. > let bygones be bygones.
