During an archeological dig at Pompeii, a worker uncovers a jewel box and the calcified body of a gladiator. En route to the Museo di Napoli, the body comes to life and kills the driver of the truck that is transporting it. Afterwards, the body, apparently dead again, is found several meters away from the wrecked truck. Without witnesses, no one fully understands what has happened.
The director of the museum, Dr. Carlo Fiorello, asks Dr. Paul Mallon to help him study the body. Fiorillo tells Paul that he is not certain that the body is in fact dead, something Paul scoffs at, even though he finds fresh blood on its hands.
Meanwhile, Dr. Emanuel translates the Etruscan writing found on a bronze brooch that was inside the jewel box. It is a curse placed on his owners by Quintillus Aurelius, the gladiator who is now the faceless monster, somehow reanimated after 2,000 years.
Tina Enright, an artist and Paul's fiancée, shows him her latest painting. It is a portrait of Quintillus, who she knows only from her dreams. Paul confirms everything that she tells him and grows worried when she says that Quintillus is coming for her.
The police investigating the truck crash discount Paul's comment that the driver's blood is literally on Quintillus's hands, and Inspector Rinaldi orders the museum closed until the murderer is caught. That night, Tina sneaks in to sketch Quintillus. He arises and walks toward her. She screams, a watchman runs in and shoots Quintillus, but the bullets have no effect. Tina faints, Quintillus kills the watchman, then places the bronze brooch on Tina's jacket. By the time help arrives, Quintillus is again immobile.
To confirm that Quintillus can move, the scientists place the brooch near him. Quintillus gets up, picks up the brooch and approaches them menacingly. Paul strikes him with an axe without making a scratch. Quintillus knocks Paul unconscious, breaks through a door and heads for Tina's apartment. When Paul recovers and everyone arrives at Tina's, they find a motionless Quintillus at her feet. Quintillus is taken back to the museum and strapped down to prevent him escaping again. His being more-or-less alive is explained by Fiorillo, who says that he was preserved by radioactivity in the volcanic ash and that he has been revitalized by the X-rays used to study him.
Emanuel takes Tina to the "Cove of the Blind Fisherman", which she says people fled into while trying to escape the volcano's ancient eruption, even though she has never heard of the cove before. Emanuel hypnotically regresses Tina and plays a recording for Paul. She says that she was the object of Quintillus' affections in ancient Pompeii, but asks "How can I return his love? I am an aristocrat. He is a slave and it is not permitted..." Stopping in mid-sentence, she then describes the eruption of Vesuvius as if it is happening. Paul remains skeptical, but Emanuel produces a photo of an ancient sculpture of a woman who looks exactly like Tina. Emanuel says that the woman was the daughter of the Roman senator who owned Quintillus.
Tina, in a trance, cuts the bonds restraining Quintillus. He carries her off to save her from what he sees in his mind – the eruption that buried Pompeii in A.D. 79. Quintillus carries her into the waters of the Cove of the Blind Fisherman. Paul, the other scientists and the police can do nothing to stop Quintillus but, to their amazement, Quintillus simply dissolves in the seawater. Paul rescues Tina, who cannot remember what happened.