The film opens with a Secret Service agent (Maurice O’Connell) who barely escapes from an English country house, in which satanic rituals are celebrated. Before he dies of his wounds, he reveals to his superiors that four prominent members of society – a government minister, a peer, a general and a famous scientist – are involved in the cult. In order to avoid any reprisals by the minister, the secret service call in Scotland Yard’s Inspector Murray (Michael Coles) to work on the case independently. Murray, who had appeared in the preceding Dracula film, suggests consulting Professor Lorrimer Van Helsing (Cushing).
The cult kidnaps the Secret service secretary Jane (Valerie Van Ost), who is later bitten by Dracula (Lee).
Murray, Secret Service agent Torrence (William Franklyn), and Van Helsing’s granddaughter Jessica (Joanna Lumley) arrive at the country house, where they discover several vampire women chained up in the cellar, including Jane who’s now a vampire herself. Murray stakes Jane and the three escape the grounds.
Meanwhile, Van Helsing pays a visit to his scientist friend Julian Keeley (Freddie Jones), whom he had recognized among the four conspirators, and finds him mentally unstable and involved on bacteriological research aiming at creating a virulent strain of the Bubonic plague. Van Helsing is shot unconscious by a guard. As he wakes up, Keeley’s dead body hangs from the ceiling while the petri dishes containing the bacteria are gone.
Keeley had referred to the 23rd of the month, which Van Helsing reveals to be the Sabbath of the Undead. Keeley’s research leads Van Helsing to the reclusive property developer D. D. Denham, who funded Keeley’s research. Van Helsing also suspects a reincarnated Dracula behind the plot, suggests that Dracula wants to exact revenge on humanity and speculates about a secret death wish on the Count’s part. Van Helsing visits Denham in his headquarters (built on top of the church yard Dracula died in the previous film) and finds out that he actually is Count Dracula. He tries to shoot Dracula with a silver bullet but is beaten by the Count’s conspirators. Dracula decides that killing Van Helsing would be too simple and has him transferred to the country house.
Meanwhile, Jessica, Murray and Torrence, while observing the country house, are attacked by snipers. Torrence is killed, while Murray and Jessica are captured. Murray awakes in the cellar and escapes the clutches of the female vampires, just as Dracula arrives with Van Helsing.
Dracula announces to Van Helsing and the ministers that Jessica, who is laid out on the satanist altar, will be his consort, uncorrupted by the plague that his “four horsemen” – including Van Helsing – would carry out into the world. The conspirators, who had considered the plague a mere deterrent, not to be used, begin to question their master but Dracula’s hypnotic command stops them and causes the minister (Richard Mathews) to break the vial, releasing the bacteria and immediately infecting the minister, causing him horrible suffering.
Murray runs into a guard in the computer room, but overpowers him after a fight scene. The guard’s metal baton smashes a computer panel and the ensuing explosion starts a fire and breaks open the ritual room. The two uninfected conspirators escape, Murray rescues Jessica, while the infected minister burns in the fire. Dracula attacks Van Helsing, who escapes through a window into the woods. He lures Dracula into a Hawthorn tree, a plant symbolising good as it provided Christ with his Crown of thorns, where Dracula is entangled until Van Helsing drives a stake through his heart.
