Donna, Donna Anderson, hosts a tense séance in Los Angeles that stretches the boundaries between belief and danger. Among the attendees is Count Yorga, Robert Quarry, a Bulgarian mystic and hypnotist who recently relocated to the United States. He had dated Donna’s mother weeks before her death and pressed for her burial rather than cremation, a detail Donna cannot quite recall seeing at the funeral.
After the gathering, Erica Landers, Judy Lang, and Paul drive Yorga home. Their van becomes trapped in mud, and Paul insists the road was dry moments earlier. With the night closing in, they accept the likelihood of spending the night in the vehicle. Yorga shows his true nature as a vampire, knocks out Paul, and drains Erica’s blood. The next day, the couple stumbles into Los Angeles with hazy memories of what happened.
Their doctor friend, Dr. Jim Hayes, Roger Perry, examines Erica’s wounds, noting the alarming loss of blood. Paul and Donna’s boyfriend Michael, Michael Macready, try to reach Erica by phone, but there is no answer. When they arrive at Erica’s home, they find a chaotic scene and a distraught Erica who has begun to lose control—she menaces Paul, then collapses into a breakdown. They restrain her and call Hayes, who begins an emergency transfusion. Erica, terrified, pleads for forgiveness and begs to be killed.
Back in Yorga’s world, his basement has become a throne room where two vampiric brides awaken, including Donna’s mother. That night, Yorga visits Erica and promises immortality as he seduces her, drains her blood, and drags her body away to his manor. Paul, alarmed by Erica’s disappearance, goes to the mansion to rescue her. There, Yorga strangles him, and his servant Brudah, Edward Walsh, breaks Paul’s back.
Michael informs Hayes that Paul has headed to the mansion. Hayes’ girlfriend suggests contacting the police, pointing to a chilling pattern of blood-drained victims, including a found baby in the woods. Hayes attempts to call for help, but the authorities dismiss him as a prankster after a rash of similar calls. Hayes, Michael, and Donna head to the mansion to keep Yorga occupied until sunrise, hoping to end the danger before it fully returns with the night.
As planned, Hayes distracts Yorga while Brudah keeps Michael from exploring too deeply. Yorga presses his guests to leave, and the trio retreats to regroup. With night falling again, Yorga reaches Donna telepathically and compels her to sabotage Michael’s alarm clock so she can lure him back to the mansion. There, Brudah rapes Donna as Yorga’s control deepens.
Michael awakens, realizes Donna is gone, and wakes Hayes. Armed with stakes and crosses, they hurry back to the mansion as darkness takes hold. The two split up; Hayes is lured into Yorga’s basement where he discovers Erica’s corpse among the other dormant brides. He engages Yorga with a cross and a stake, shouting for Michael, but Yorga awakens the brides to attack Hayes.
Donna is reunited with her mother as Michael finds Paul’s mutilated body and Brudah mortally wounds him. In the basement, Hayes reveals Donna’s location before dying. Erica and the other bride awaken fully to attack Michael, but he manages to stake Erica—yet he cannot bring himself to kill her, leaving her alive but transformed.
Michael confronts Yorga and Donna’s mother, with Yorga pushing her into his stake and fleeing. Michael ultimately defeats Yorga with a stake, and Donna mourns her mother once more as Michael helps her move forward.
As they prepare to depart, Erica and the remaining bride descend upon them. The pair is driven back by Michael’s crosspower, forced into a cellar, and locked away. But when Michael lowers his guard and Donna—now fully turned—descends upon him, she lunges and kills him, sealing a grim fate as the night closes around them.
