Count Alucard is invited by Katherine Caldwell to the United States. Colonel Caldwell dies soon after his arrival, and his wealth is shared between his two daughters: Claire Caldwell inherits the money, while Katherine inherits the estate known as Dark Oaks. Katherine has been secretly seeing Alucard, and the two are quickly married, a union that unsettles everyone around them.
Her former long-time fiancé, Frank Stanley, confronts the couple and tries to shoot Alucard. The bullets pass through the Count’s body and strike Katherine, leaving her seemingly dead. A shaken Frank rushes to tell Dr. Harry Brewster what has happened, hoping the doctor can confirm the worst. Yet at the doctor’s arrival, he is confronted not with a corpse but with a living Katherine and a menacing Alucard. The couple declares that they will devote their days to scientific research and will only receive visitors at night, casting a chilling aura over Dark Oaks.
Frank, believing Katherine is dead, goes to the police and confesses to the murder. The Sheriff is reluctant to believe the tale of a living vampire, but Brewster tries to convince him otherwise, insisting that Katherine is alive. A search of Dark Oaks ensues, and Katherine’s body is found and moved to the morgue, sealing Frank’s fate as he is charged with murder and jailed.
Meanwhile, at Brewster’s house, Professor Lazlo arrives and helps articulate the bloodthirsty mystery. Lazlo quickly suspects vampirism and suggests that Alucard could indeed be Count Dracula himself. The tension escalates when Alucard materializes and attacks Brewster, only to be driven back by Lazlo’s crucifix. A local boy’s testimony confirms bite marks on young necks, reinforcing the vampire theory and tightening the noose around the surreal crime.
Katherine later sneaks into Frank’s cell and reveals that she only married Alucard to gain immortality and wants to share that gift with Frank, her true love. He is initially repulsed by the idea, but eventually yields. She explains that she has already drunk some of his blood and guides him on how to destroy Alucard. Frank breaks out of custody, seeks out Alucard’s hiding place, and burns his coffin, cutting off the vampire’s daylight sanctuary.
As dawn approaches, Alucard is destroyed when the sun rises, and Brewster, Lazlo, and the Sheriff arrive to confirm the vampire’s remains. Frank, weary but resolute, continues his vigil in the haunted playroom where Katherine once spoke of immortality; he discovers the moment of truth as he finds Katherine’s coffin and, with a heavy heart, places his ring on Katherine’s left finger. When Brewster and the others reach the room, they glimpse Katherine’s burning coffin, and Frank stands by, muted by grief, bearing witness to the profound loss of the woman he loved.
