In 1780, Mamuwalde, an African prince, travels to Transylvania to seek the help of Dracula in ending the slave trade. Dracula refuses, and insults Mamuwalde by flirting with his wife Luva. After a clash with Dracula's minions, Mamuwalde is bitten and transformed into a vampire. Dracula then curses him with the name "Blacula" and imprisons him in a sealed coffin beneath his castle, while Luva dies in the chamber from suffocation or starvation.
Fast forward to 1972, two interior decorators, Bobby McCoy and Billy Schaffer, purchase the coffin and ship it to Los Angeles. They open it, becoming Blacula's first victims. At the funeral home where McCoy's body lies, Blacula spies on Tina Williams, Tina Williams, her sister Michelle, and Michelle's boyfriend, Dr. Gordon Thomas, a pathologist for the LAPD. Blacula becomes infatuated with Tina, believing her to be the reincarnation of Luva. Dr. Thomas notices oddities with McCoy's death, which he suspects are linked to vampire folklore. Blacula follows Tina after leaving the funeral home but frightens her, and a cab hits him, though he then kills the cab driver Juanita Jones.
Thomas, Michelle, and Tina celebrate Michelle's birthday at a nightclub, and Blacula appears to return Tina's purse. Thomas answers a call from the funeral director about McCoy's missing body. Blacula asks Tina to see him again the next evening, but they are interrupted by Nancy, a photographer who snaps a photo of them together. Blacula kills Nancy and destroys the photo she developed, which shows Blacula in the frame. The next evening, Blacula visits Tina at her apartment and shares how Dracula enslaved him, and how he was cursed with vampirism. They spend the night together.
Thomas, Lt. John "Jack" Peters, and Michelle begin following the murders. Thomas deduces that a vampire is behind them. After they dig up Schaffer's coffin, the corpse rises and attacks Thomas; he fends it off and drives a stake through its heart. Michelle realizes McCoy could still be out there. To prove it, they thaw Juanita Jones's body. Thomas instructs Sam, the morgue attendant Sam, to take Jones's body out and leave the room. Sam, distracted by a phone call, fails to lock the door, and Jones's body rises and attacks him. Thomas and Peters arrive at the morgue to find blood smeared on the wall but no sign of Sam. They uncover the sheet-covered body on a gurney—Jones rises to attack, and Thomas uses a Christian cross and opens the blinds to expose her to sunlight, destroying her.
That evening, Blacula hypnotizes Tina to join him at a new hideout at an underground chemical plant, while Thomas and the police close in. Blacula evades capture but an officer fatally wounds Tina with a stray shot. To save her life, Blacula transforms Tina into a vampire. Blacula fights the pursuing police, and a finder locates the coffin. Peters then kills the newly transformed Tina with a stake, believing Blacula would be in the coffin. Devastated and without a clear purpose, Blacula takes his own life by climbing to a roof as the morning sun destroys him. Thomas and Peters witness his flesh melt away, maggots spilling from the face, leaving only a skeleton.
