It stars Scott Brady, Virginia Mayo, David Brian, Lisa Gaye, Hugh Marlowe and William Thourlby.

Castle of Evil tells the story of a dead scientist who, with the help of his long-time housekeeper and a robot, seeks revenge from beyond the grave on the person who murdered him.

The undertaker Muchado has been called to Castle Montego by housekeeper Lupe Tekal d'Esperanza because of the death of her employer, the reclusive scientist Kovic.

Lupe pays him, poisons him and disposes of his body in a disintegrator chamber in the castle's secret laboratory.

A boat arrives at the castle, on an island near Nassau, with six people: Matt Granger, Sable, Robert Hawley, Carrol, Doc Corozal and Tunki.

However, the film was licensed by World Entertainment Corp. to 13 television stations in "several western states" months before it opened in theaters across the US.

American critic and psychometrist Bryan Senn writes the reason that "the awful (but color) Castle of Evil" ran first is because Blood Beast from Outer Space was "shot in moody black and white when, at the time, even low-budget efforts were almost invariable in color.

[7][8] The exhibitor's manual for Castle of Evil and Blood Beast from Outer Space describes the double bill as the "Twin Shock Show With That Big Box-Office Punch!

British Critic Phil Hardy calls the movie a "tedious film" in which "A murderer's robot (...) is programmed to kill the members of the trio responsible for disfiguring the scientist before his death."

"[15] Clive Davies, a British critic, writes that "This kind of senseless horror with old dark house mystery trappings is not very good, but is strangely enjoyable."

He, too, makes note of the film's "robotic electronic clone" of Kovic, the laser gun and "A gas chamber in the basement [that] turns people into skeletons instantly.

"[16] Another American critic, Kristie Hanssen, describes the plot of Castle of Evil as "A bunch of hopeful heirs arrives on an isolated island to hear the will of a horribly scarred, mad scientist."

Besides finding the person who caused Kovic's disfigurement, they must "also survive the rampages of a robot the scientist made in his own image.