[4] The screenplay was by Christopher Wicking, based on the 1967 novel The Disorientated Man, attributed to "Peter Saxon", a house pseudonym used by various authors in the 1960s and 1970s.

In London, Metropolitan Police Detective Superintendent Bellaver investigates the rape and murder of a young woman, Eileen Stevens.

WPC Helen Bradford, wearing a wire and electronic tracer, goes to the same club where she lets herself get picked up and driven away by Keith.

The narrative strands begin to come together when a senior UK Government officer, Fremont, meets Konratz at London's Trafalgar Square, and agrees to turn over all the evidence in exchange for a captured pilot.

Back at the laboratory, Sorel discovers Browning is about to dismember Bradford, as part of a plot to replace humans with composite beings.

[5] The edits also cut scenes of actors Julian Holloway and David Lodge as police detectives, though they are still listed in the credits.

Rights to the novel were bought by Milton Subotsky of Amicus Productions, who got financing from Louis Heyward, head of European operations for AIP.

The film was made in the span of a month, starting 5 May 1969 at Shepperton, with location work done at Trafalgar Square and Chertsey, Surrey.

[9] The Monthly Film Bulletin wrote: "A plot has been crudely put together with the incongruously clearcut and matter-of-fact tone of a crime thriller ... and the three personalities slotted in at the appropriate places.

To justify two of the stars, the theme of vampirism slides, ominously and unnecessarily, in and out of the film, and the creation of a whole race of man-made monsters is now accomplished by a more advanced science than Dr. Frankenstein's ... Vincent Price, hypersensitive recluse and dabbler in the occult, is the menacingly affable director of the clinic where events, and the new supermen, all begin.

Not surprisingly, the triumvirate have little room to manoeuvre inside the tight fit of their functional clichés: Peter Cushing has the least opportunity (little more than a bit part), while Christopher Lee disappears into a greying nonentity of a civil servant, failing to emerge even with the final revelation of masked depravity.

Vincent Price inimitably delivers the most banal dialogue with a disconcerting relish, though the giveaway decadence of Dr. Browning's living quarters, keyed to a pretty shade of pastel pink, would have provoked a creeping horror in Roderick Usher.

"[10] Howard Thompson of The New York Times wrote that the film "tools along intriguingly for a while with some genuine possibilities before taking a nosedive", when it "ends up in still another mad scientist's lair".

"[12] Roger Ebert of the Chicago Sun-Times gave the film two stars out of four, calling it "ridiculous", yet "impossible to dislike because they ask only that you share their sense of the absurd.

"[14] Kevin Thomas of the Los Angeles Times called the film "a superb piece of contemporary horror, a science fiction tale possessed of a credibility more terrifying than any of the Gothic witchery of Rosemary's Baby ...