Christopher Hatton owns the country estate, Moderlaine. While Hatton's son Barney has a romantic tryst with Dilys Helmar, Hatton loses his estate in a game of decide to Dilys' father Nick.
The Hattons are forced to move to a cottage in a nearby village. One day Barney sees some villagers attacking a young woman, whom he rescues. She is Jassy Woodroffe, daughter of Tom Woodroffe and a gypsy mother. She has the gift of second sight which causes the villagers to regard her as a witch.
Mrs Hatton hires Jassy as a domestic servant. Meanwhile, blacksmith Bob Wicks whips his daughter Lindy so badly she becomes mute.
Nick Helmar and his family move into Moderlaine. Nick allows Christopher Hatton to continue gambling. When Hatton is caught cheating, he kills himself.
Nick finds his wife has been having an affair and asks for a divorce.
Tom Woodruffe leads a crowd of villagers to march on the Helmars, who are now their landlords, to demand better pay and conditions. Back in the village, Jassy senses something bad will happen and asks Barney to help. A drunken Nick confronts Tom and accidentally shoots him.
Jassy and Barney become close which worries Barney's mother. She sends her to a ladies' finishing school where she becomes friends with Dilys Helmar. Dilys sneaks out for a romantic tryst one night and when Jassy covers for her, Jassy is sacked.
Dilys takes Jassy home with her to Moderlaine. Nick tells Jassy that he killed her father.
Dilys and Jassy go to see Barney. Dilys and Barney resume their romance, which upsets Jassy, who still loves Barney and knows that Dilys is also seeing Stephen Fennell.
Nick offers Jassy the job of running Mordelaine. Jassy restructures of the staff, hiring Lindy at the recommendation of Mrs Wicks.
One day, Jassy catches Dilys and Stephen together. Nick horsewhips Dilys, who runs out into the arms and carriage of Stephen. Barney goes to see Stephen and finds that he and Dilys are engaged.
Nick proposes marriage to Jassy, who eventually agrees when he agrees to give her Mordelaine as a wedding gift. They marry, but Jassy insists on living separately. In a fury, Nick goes out riding and has an accident.
He is brought back to Mordelaine, where the doctor prescribes a strict diet and no alcohol, which Jassy enforces, even though Nick is increasingly violent towards her. When Jassy goes to visit Dilys and Stephen, Lindy decides to poison Nick for what he's done to Jassy, slipping rat poison into a bottle of wine.
Nick's murder is sensed by Jassy, who cries out that he's dead. Stephen thinks that she murdered him, and has her arrested along with Lindy.
At the trial, despite Jassy's alibi, the pair are found guilty, but the shock goads Lindy into speech. She confesses to the murder, exonerates Jassy, and drops dead.
Jassy signs over Mordelaine to Barney, its rightful heir, and the reunited couple kiss.Margaret Lockwood as Jassy Woodroofe
Patricia Roc as Dilys Helmar
Dennis Price as Christopher Hatton
Basil Sydney as Nick Helmar
Dermot Walsh as Barney Hatton
Esma Cannon as Lindy Wicks
Cathleen Nesbitt as Elizabeth Twisdale
Linden Travers as Beatrice Helmar
Nora Swinburne as Mrs. Hatton
Ernest Thesiger as Sir Edward Follesmark
Jean Cadell as Meggie
Grace Arnold as Housemaid
John Laurie as Tom Woodroofe
Bryan Coleman as Sedley – the architect
Clive Morton as Sir William Fennell
Torin Thatcher as Bob Wicks
Beatrice Varley as Mrs. Wicks
Eliot Makeham as Moult – the butler
Maurice Denham as Jim Stoner
Alan Wheatley as Sir Edward Walker – Prosecuting Counsel
Hugh Pryse as Sir John Penty – Defending Counsel
The film was based on a novel by Norah Lofts, originally published in 1944. Film rights were bought by Gainsborough Pictures who in 1946 saw Maurice Ostrer replaced as head of production by Sydney Box. In his last years, Ostrer had specialized in making melodramas that had been highly lucrative to the studio, many of which starred Margaret Lockwood. Box wanted to expand the variety of Gainsborough's output, but when he arrived Jassy was the only script ready to go into production. It would have been more expensive to let the sound stages go idle so the film went ahead. In August 1946 Box announced Gainsborough would make Jassy.
By this stage Gainsborough had lost the services of a number of people crucial to the success of the Gainsborough melodramas, including Leslie Arliss, Ted Black, Maurice Ostrer, Harold Huth and R.J. Minney.
John Cromwell was originally announced as director.
The film was given a large budget. It was considered a "special", i.e. one of the most expensive made by Gainsborough, and the first film shot in Technicolor there.
According to Dermot Walsh "they offered the part of my father to Peter Graves who turned it down on the grounds that playing father to a twenty one year old boy would make him look too old. So poor old Denis [Price] was trundled out."
Susan Shaw has a small role. Wilfred Bramble:_ is one of the servants
The film was the seventh most popular movie at the British box office in 1947. By 1953 Jassy had earned net revenue of £200,000 and its box office performance was described as "excellent".
This encouraged Sydney Box to make two more costume film "specials", Bad Lord Byron and Christopher Columbus, the financial failure of which ended the cycle.
The Los Angeles Times liked the photography but criticised the acting and direction.
The New York Times said that:
With plot ramifications providing for infidelity, suicide, murders and a gypsy beauty endowed with second sight, it would seem that "Jassy" would add up to a swift and exciting movie. But this period piece, brilliantly accoutered in Technicolor and imported from England to begin a stand at the Winter Garden yesterday, is unimaginative drama, hampered rather than helped by its story lines and not too greatly aided by some broad and stylized characterizations. Boiled down to essentials, "Jassy" is a combination of several plots, mostly familiar, the sum of which makes for a rather rambling and routine entertainment.