HOUSE OF DARK SHADOWS

Willie Loomis, the Collins family handyman, is searching for old treasure in the family mausoleum when he accidentally frees Barnabas Collins, a 175-year-old vampire who enslaves him. Upon his release, he attacks Daphne Budd, the secretary to Collinwood's matriarch, Elizabeth Collins Stoddard. She is discovered by Jeff Clark, who takes her back to the house where Dr. Julia Hoffman attends to her.

Later, Barnabas introduces himself to the family under the guise of a "cousin from England". Elizabeth and the others are intrigued by Barnabas and take an instant liking to him. However, Elizabeth's daughter, Carolyn Stoddard, and Professor T. Eliot Stokes, a friend of the family, are incredulous. Barnabas insists on moving into the Old House and hosting a ball in honour of the family. But on the night of the ball, Carolyn is bitten by Barnabas while she is getting ready.

Later on at the ball, he is introduced to young David Collins' governess and Jeff's girlfriend, Maggie Evans, and is instantly smitten with her, as she bears a striking resemblance to his long-lost fiancée, Josette du Pres. Maggie is thinking about leaving Collinwood, but Barnabas persuades her to stay. Back at the Old House, he tells Willie about Josette and how she took her own life on the night they were to be married. Carolyn overhears and, out of jealousy, threatens to expose him . Enraged, Barnabas delivers a deadly bite to Carolyn, much to Willie's horror. A shaken Willie takes Carolyn back home; she slowly walks to the doorway, but she is soon discovered slumped in the doorway—dead—by the housekeeper, Mrs. Sarah Johnson.

Funeral services are held for Carolyn, and she is buried in the Collins family mausoleum. Dr. Hoffman, upon analyzing samples of Carolyn's blood, recognizes a trace of elements of the same unknown virus that was present in Daphne Budd's blood sample. Thereafter, Professor Stokes confers with Julia and tells her that he suspects that the recent attacks in Collinsport may have been caused by a vampire. Julia is initially skeptical but soon becomes an ally of Stokes when he informs the family of his theory.

Meanwhile, Carolyn rises as a vampire and menaces David. Stokes and Julia try to explain, but Elizabeth and her brother Roger Collins refuse to listen. Carolyn's fiancé, Todd Blake, encounters her, and she bites him. After he is taken back to Collinwood, the family realizes that Stokes and Julia were correct about the vampire. Todd again sneaks out in search of Carolyn, but she is cornered and staked, instantly destroying her.

Julia eventually discovers that Barnabas is the vampire responsible. Thus, she visits him at the Old House and convinces him that she can use modern-day medicine to make him human, and he reluctantly agrees. Julia gives him injections that allow him to walk in the daylight and apparently no longer need to ingest human blood to survive. Over time, Barnabas and Maggie begin to spend time together while Jeff is away in Boston. Stokes confronts Julia about helping Barnabas—and realizes she is in love with him—and reminds her that he is in love with Maggie. Overcome with jealousy, Julia gives Barnabas an overdose of her serum, which causes him to age rapidly to his true age, 175 years. In a rage, he strangles her to death. A terrified Maggie witnesses this and tries to flee, but is caught and bitten by Barnabas before she can escape, and he vows to come back for her. Jeff soon returns, and he is informed of the family history by Stokes and Roger and that Barnabas intends to make Maggie his bride. That night, Barnabas bites Maggie again, rejuvenating him, and then abducts her.

Jeff and the others pursue them; however, Roger and Stokes are killed (both turned into vampires whom Jeff destroys). Jeff eventually finds Maggie at an old church in a trance and in Josette's wedding gown. Willie warns him against trying to stop Barnabas and knocks him out. Willie leads Maggie out of the room to where Barnabas is waiting for her. He lays her down on an altar and is about to bite her when Jeff wakes up and shoots at him, but Willie, running to stop Barnabas, moves in the way, and is hit by Jeff's crossbow bolt. Barnabas lures Jeff out of his hiding place and forces him to be a witness by placing him in a trance. However, as Barnabas again attempts to bite Maggie, he screams in pain as he's struck in his back. Turning around, he's shocked, then enraged, to discover that Willie—in his final act of redemption—had stabbed him with the crossbow bolt. Barnabas strangles the mortally wounded Willie, but Loomis's attack breaks Jeff out of Barnabas's trance long enough for Jeff to finish driving the bolt through the vampire's back, ultimately bursting through his bloody chest. Maggie, now no longer entranced, is rescued by Jeff, both briefly observing the bodies of the presumably dead vampire and Willie Loomis before departing the ruined chapel.

In a post-credits scene, Barnabas's body transforms into a bat and then flies away.

Barnabas Collins is ultimately confronted and destroyed after wreaking havoc on the Collins family and those around them, ending his reign of terror at the estate.

The film resolves its central conflict by eliminating Barnabas, the supernatural threat, restoring a fragile peace to the Collins family and their estate. This climax underscores the gothic theme that old family secrets and curses, no matter how deeply buried, will resurface and demand reckoning. The conclusion ties together the film’s motifs of lost love, betrayal, and the high cost of obsession.