The film opens on a small farm in Greenwich, Connecticut in 1844. Farmer's daughter Miranda Wells (Gene Tierney) is brought up by her strait-laced low church parents, Ephraim (Walter Huston) and Abigail (Anne Revere). Miranda, a budding young woman, lives on the farm with her family, but often escapes everyday life on the farm through daydreams of a more romantic location and lifestyle, filled with luxury and flair.
When Miranda’s mother Abigail receives a letter from a distant cousin, Nicholas Van Ryn (Vincent Price), Miranda is thrilled by the news. The autocratic, charming and atheistic Nicholas is the owner of Dragonwyck Manor, an exclusive estate with extensive lands and a luxurious mansion. The estate is quite the envy of his fellow Hudson River landholders. In the letter, Nicholas asks if one of Abigail’s daughters could come and serve as governess for his eight-year-old girl Katrine (Connie Marshall). Abigail tells Miranda that Nicholas is descended from the original Dutch patroons, yet Abigail is dubious, and the devoutly religious Ephraim is opposed.
Miranda is eager to go, and shows her father a Bible passage that sways him. Before long, Ephraim and Miranda meet Nicholas as he arrives to the farm. Despite Nicholas’s arrogance toward the Van Ryn tenant farmers, Ephraim relents enough to let Miranda go. Nicholas is attracted to Miranda. When they reach Dragonwyck, Nicholas presents the lovely Miranda to his daughter Katrine and his gluttonous wife, Johanna (Vivienne Osborne). Despite high hopes, Miranda finds the Van Ryns a bit strange. The parents barely know daughter Katrine; Nicholas faces a revolt of his tenant farmers; the servants hint darkly of curses and visitations.
One afternoon, Miranda and Katrine hide in the woods to watch the ”kermess” — an annual ceremony at which Nicholas receives the rents of his tenants. Dr. Jeff Turner (Glenn Langan) discovers the girls, is immediately attracted to Miranda, and expresses his interest in seeing her again. He manages to utter that he is not fond of the arrogant autocrat Nicholas. He claims that Nicholas is feudal in his way of thinking, not compatible with the doctor’s own egalitarian principles.
During the kermess, a farmer, Klaas Bleeker (Harry Morgan), claims that he and his family have paid Nicholas so much rent that the farmer ought to own the land many times over, and says he refuses to pay more rent. Nicholas regards the farmer as insubordinate and immediately evicts him from the farm.
Klaas tries to attack Nicholas, but Jeff steps between them and prevents either one from hurting himself or the other. Jeff defend Klaas's political position. That evening, Nicholas hosts a ball at his mansion, and some of the high society guests snub Miranda and her humble farming background, upon which she feels both inadequate and enraged.
Shortly thereafter, Jeff arrives at Dragonwyck to ask for help in defending Klaas, who has been falsely accused of murder. Nicholas is not interested at first, but eventually promises to help, and then asks Jeff to examine Johanna, who has caught a head cold. Jeff does so and assures her that the cold will pass. Then he joins Miranda for a romantic dinner.
That night Nicholas brings his favorite oleander plant to Johanna's room to cheer her up, and stays to give her some cake. Later in the night, Johanna dies suddenly, much to Jeff's astonishment, since she was well on her way to getting better. Nicholas meets Miranda downstairs and tells her that he was never happy with his wife Johanna, and she could not bear him a much longed-for son.
Miranda has been attracted to Nicholas since she first met him, and when hearing this confession from Nicholas, she can no longer fight her feelings. She caves in and the couple admit their love for each other, although Miranda returns to Connecticut the next day.
Miranda does her chores at the farm every day, but appears distant and dreamy, and Ephraim is irritated with her. He doesn't get an explanation for her behavior until two months later, when Nicholas arrives and asks for her hand in marriage. Ephraim and Abigail reluctantly consent, not being very fond of the snob, and a few months later, Nicholas is away on business when Miranda discovers that she is pregnant. Despite their quarrels over Nicholas' lack of religious faith and his fury over Miranda's hiring of a lame maid, Peggy O'Malley (Jessica Tandy), Nicholas is thrilled by the news.
However, Nicholas' joy over the pregnancy is somewhat tempered by a set of new laws, permitting tenant farmers to buy their lands. Despite this threat to his historic rights, he counts on passing Dragonwyck on to the baby, who he is sure will be a son. Nicholas asks Jeff to take care of Miranda when she gives birth. Jeff is pleased to see Miranda, whom he still loves, but after examining her, he tells her that her newborn son has a defective heart. The boy is hardly born before he dies, but Miranda has the baby baptized before he dies.
Nicholas is upset and heartbroken by his son's death. During the next few months he grows more distant and embittered. He starts using illegal substances to dampen his despair, and eventually confesses his addiction to Miranda. The goodhearted Peggy starts fearing for her mistress' life, since Nicholas has become more unpredictable and unstable. Peggy begs Jeff for help, telling him about the oleander plant Nicholas has brought up to Miranda's room.
Jeff panics and rushes to Dragonwyck, accusing Nicholas of poisoning Johanna with oleander and now attempting to do the same to Miranda. Much to Miranda's horror, Nicholas admits his crime against his former wife and attacks Jeff, trying to kill him. Jeff manages to knock down Nicholas during the struggle, which makes it possible for Jeff and Miranda to leave the premises. Nicholas wakes up, staggers over to the kermess grounds, and calls for the farmers to bring their tributes, waving a pistol around.
All the farmers come man-out-of-house and gather around Nicholas. Jeff, Miranda, the mayor and sheriff arrive. Nicholas takes aim at Jeff with his pistol and is shot. Nicholas dies in front of the crowd, and the farmers doff their caps. Miranda prepares to return to Greenwich, realizing it is her true home. Jeff sees her off and promises to visit her the following week.Gene Tierney as Miranda Wells
Vincent Price as Nicholas van Ryn
Walter Huston as Ephraim Wells
Glenn Langan as Dr. Turner
Anne Revere as Abigail Wells
Spring Byington as Magda
Harry Morgan as Bleecker
Jessica Tandy as Peggy
Vivienne Osborne as Johanna Van Ryn
Trudy Marshall as Elizabeth Van Borden
Bosley Crowther of the New York Times said: "...Twentieth Century-Fox has fashioned a grand and gloomy mansion as the scene and has inhabited it with a haughty master of aristocratic Dutch descent. ... Vincent Price gives a picturesque performance as the regal and godless patroon, using his face and his carriage to demonstrate insolence, that's all. Clean shaven and elegantly tailored, he still makes a formidable Bluebeard, and his moments of suave diabolism are about the best in the film. Gene Tierney is fairly ornamental in the role of the tortured child bride, but she plainly creates no more character than the meager script provides. Of the several lesser characters, Walter Huston is most credible as the forthright, God-fearing father of the cardboard heroine."
Dragonwyck was adapted as an hour-long radio play on the October 7, 1946 broadcast of Lux Radio Theater, starring Vincent Price and Gene Tierney. It was also dramatized as a half-hour radio play on the January 20, 1947, broadcast of The Screen Guild Theater, starring Vincent Price and Teresa Wright.