In the Collins family mausoleum, Willie Loomis unearths old treasure and accidentally frees Barnabas Collins, a vampire who has haunted the family for centuries and quickly asserts control over him. Upon his release, Barnabas attacks Daphne Budd, the secretary to Elizabeth Stoddard Collins, leaving Daphne gravely wounded and prompting Jeff Clark to rush her back to Collinwood for care, where she is tended to by Dr. Julia Hoffman. The danger in the house deepens as Barnabas insinuates himself into the family’s life, weaving a web of charm and menace.
Barnabas introduces himself to the clan as a “cousin from England,” and the household is intrigued by his suave manner and eerie aura. Yet Carolyn Stoddard and the family’s scholar, Professor T. Eliot Stokes, remain skeptical, sensing something unsettling beneath his behavior. Despite initial misgivings, Barnabas persuades the household to allow him to move into the Old House and even hosts a formal ball in honor of the family. On the night of the celebration, Carolyn is bitten by Barnabas, revealing the true danger behind the charming veneer.
At the ball, Barnabas meets the young Maggie Evans, the governess to David Collins and the companion to Jeff’s life, and he is instantly drawn to her—she bears an uncanny resemblance to his long-lost Josette. Maggie herself contemplates leaving Collinwood, but Barnabas convinces her to stay for a while. Back at the Old House, Barnabas opens up to [Willie Loomis], recounting the tragedy of his lost love Josette and the night of their supposed wedding. Carolyn overhears this confession and, driven by jealousy, threatens to expose him. Enraged, Barnabas delivers a deadly bite to Carolyn, and she dies in a grim moment that shocks Willie into action, taking Carolyn back to the house where the housekeeper eventually discovers her lifeless body.
Funeral rites follow, and Dr. Hoffman, studying samples of Carolyn’s blood, detects traces of elements identical to those found in Daphne Budd’s blood. This discovery convinces Professor T. Eliot Stokes that a vampire may be behind the recent town attacks, and he shares his concern with Julia, who begins to see the possibility as well. Carolyn’s corpse is later revived as a vampire, menacing David and forcing the family to confront the bloodthirsty reality of Barnabas’s presence. Carolyn’s fiancé, Todd Blake, encounters her and is bitten, leading the family to confront the frightening truth that Stokes and Julia may be right about the danger in their midst.
Todd is brought back to Collinwood, and the fear intensifies as the family realizes that Carolyn’s incursion into vampirism is only one part of Barnabas’s larger plan. He pursues Maggie with a renewed fervor, intent on making her his bride, and the household braces for more bloodshed. Todd’s pursuit ends in tragedy, as he is eventually stalked and killed after a second bite. Meanwhile, Julia’s role in Barnabas’s life grows increasingly complicated: she helps him regain mobility with a serum that allows him to walk in daylight and seemingly Live without needing to feed on human blood. Barnabas and Maggie begin to spend time together, even as Jeff travels to Boston, and the evolving dynamic deepens the tension in Collinwood.
Jealousy's shadow falls over Julia as she confesses her love for Barnabas and resents Stokes’s presence in Maggie’s life. She discreetly administers an overdose of her serum, causing Barnabas to age to his true 175-year-old self. In a fit of rage, he strangles Julia, and Maggie, who witnesses the murder, fears she will be next. Barnabas then renews his attack on Maggie, biting her again to restore his vitality and abduct her to seal his impending union with her.
Jeff and the others press their search, and a climactic confrontation ensues. Roger Collins and Stokes fall in battle, both transformed into vampires, and Jeff destroys them. Jeff eventually locates Maggie in a ruined church, where she sits in a trance, dressed in Josette’s wedding gown. Willie Loomis warns Jeff against interfering, but Willie’s loyalty to Maggie—and his deep wish to redeem himself—drives him to intervene. He lures Maggie away to a hidden altar, where Barnabas awaits; Jeff shoots to break the trance, but Willie sacrifices himself, charging into Barnabas’s path and taking a fatal crossbow bolt intended for Maggie. Barnabas, enraged and murderous, strangles the dying Willie, while Jeff finishes the conflict by driving the crossbow bolt through Barnabas’s back, ripping a bloody chest wound that ends the vampire’s threat.
With Barnabas defeated and Maggie rescued, the two survivors depart the shattered church, the town’s nightmare temporarily at an end. In a final, post-credits flash, Barnabas’s body twists into a bat and disappears into the night, leaving the mysterious curse of Collinwood hanging in the air and the memory of a family’s struggle against an ancient darkness.
