For 20 years, unrepentant Nazi scientist Dr. Norberg (Dana Andrews) has been experimentally thawing frozen Nazi soldiers who have been kept in suspended animation at his English country estate since the end of World War II. He is awaiting his superiors, General Lubeck (Karel Stepanek) and Captain Tirptiz (Basil Henson), who have been told by Norberg's assistant, Karl (Alan Tilvern) that Norberg's experiments have been a complete success. Unfortunately, they have not been. Norberg can thaw the body, but not the brain. All that he can produce are zombie-like beings who can do no more than endlessly repeat the memory of just one action from their past. The worst of them, Prisoner no. 3 (Edward Fox), is extremely violent, and is Norberg's brother.
Lubeck tells Norberg that 1,500 frozen Nazis have been stashed in several countries. In order to revive the Third Reich, Lubeck exclaims that they are 'to be restored to full capacity at the right time - which is now!' To help do this, Norberg brings in American scientist Ted Roberts (Philip Gilbert), who has had some success in thawing functional brains. Ted, unaware of the Nazi plot, believes that he is to help Norberg keep organs alive for medical use.
Norberg's niece, Jean (Anna Palk) arrives home unexpectedly from a university in America, bringing along her friend Elsa (Kathleen Breck). On the day after they arrive, Elsa leaves on the 6:00 AM train to London without telling Jean. Jean does not understand her sudden departure.
Norberg tells Ted that he plans to experiment on a monkey's head, keeping it alive, with a clear plastic dome over its cranium so that he can observe its brain function, then transfer what he learns to humans. Ted readily agrees to help. But then Norberg unexpectedly has the opportunity to use a human head, for Karl had drugged Elsa and taken her to the laboratory, not the train station. Norberg and Karl find Elsa dead in the lab, with Prisoner no. 3 standing over her body, smiling.
Norberg later impresses Ted with a wall of amputated human arms, which he can control through electrical stimulation. After Ted agrees to tell no one of what he is about to see, Norberg trustingly shows him Elsa's head, alive, its skin a horrid blue color and its brain covered by a clear plastic dome.
That night, Jean has a nightmare. She tells Ted that she has dreamed that Elsa is dead and that her head is in the laboratory. To keep from further upsetting her, Ted dismisses it as just a bad dream. In truth, Elsa is communicating telepathically with Jean as she sleeps. Not knowing this, Jean persists in trying to find her friend, consulting railway station personnel and a Mrs. Smith (Ann Tirard), who may know something about Elsa's whereabouts. Mrs. Smith denies any knowledge of Elsa, but she is, in reality, Mrs. Schmidt, another Nazi living undercover in England. Jean does not discover this and asks Police Inspector Witt (Tom Chatto) to investigate.
After seeing Elsa's head, Ted wonders about Norberg's real intent. As he walks toward the lab, Karl knocks him unconscious. When he comes to, Norberg tells him that he was attacked by Norberg's brother, whom Norberg describes as having been 'mentally ill' since the war. He asks Ted not to tell Jean, as no. 3 is her father and she has believed since childhood that he died in a concentration camp, not a Nazi but a victim of the Nazis.
Lubeck and Tirptiz torture Karl to find out if he has told anyone about their plot. He confesses that he has told the Schmidts, who are members of his own family. After Karl tries to prove his loyalty to the Nazis by attempting to murder Jean and Ted, Lubeck forces Norberg to freeze Karl as punishment.
Norberg tries to demonstrate to Lubeck and Tirpitz that Elsa can control the wall of arms, but nothing happens. Ted suggests that Elsa still has will power. Norberg scoffs at the notion. Lubeck and Tirpitz, by now afraid that Jean will find out about the plot, discuss killing Jean as Elsa listens.
That night, Elsa again communicates telepathically with Jean, who, in a trance, heads for the lab. Ted rouses her at the locked door. Jean is certain that Elsa is inside and convinces Ted that Elsa needs their help. Ted tells Jean that no. 3 is actually her father. She sends Ted to get Witt, then steals the key to the lab and finds Elsa. Norberg confirms that no. 3 is Jean's father, but when he says that no. 3 killed Elsa, Elsa tells Jean that Karl killed her.
Lubeck reveals the Nazi plot to Jean. When he draws a pistol to shoot her, he and Norberg struggle over it in front of the wall of arms. Elsa activates the arms, which strangle them both. Meanwhile, Jean runs to see her father. Tirpitz appears just in time and shoots Prisoner no. 3 dead as he is strangling her.
Finally, with Jean, Ted and Witt looking on, Elsa pitifully whimpers 'Bury me' over and over again.
