A newlywed deputy, Martin Gordon (Vic Savage), encounters an alien spacecraft that has crash landed in fictional Angel County in California. A large, hairy, slug-like, omnivorous monster emerges from the side of an impacted spaceship. A second one, still tethered inside, kills a forest ranger and the sheriff (Byrd Holland) when they independently enter the craft to investigate.
Gordon, now a temporary sheriff, joins his wife Brett (Shannon O'Neil). Dr. Bradford (William Thourlby), a renowned scientist, Col. James Caldwell (John Caresio), a military commander, and Caldwell's men were sent to fight the creature. Meanwhile, the monster stalks the countryside, devouring a girl in a bikini, picnickers at a "hootenanny", Grandpa Brown (Jack King) and his grandson while fishing, a housewife hanging the laundry, the patrons at a community dance hall, and couples in their cars at a lovers' lane.
The protagonists deduce that the monsters are mindless biological-sample eaters. The bio-analysis data is microwaved back to the probe's home planet through the spaceship.
Caldwell decides that the creatures must be killed, despite Bradford's objections. He orders his men to fire at the creature, which they do while standing close to one another as it moves towards them. Their gunfire proves ineffective, and all of the troops are devoured. Paradoxically, Caldwell decides a moment later to throw a grenade, and the creature dies instantly.
Ultimately, both creatures are destroyed, but not before the signal is sent. The dying Bradford suggests that this bodes ill for the human race, but observes that, since the galaxy to which the transmission was aimed is a million light years away, the threat may not manifest itself for millennia.
The Creeping Terror was directed, produced and edited by Vic Savage under the alias A. J. Nelson. Although Robert Silliphant is the credited writer, the original story was written by his younger brother, Allen. Silliphant's half-brother, Stirling, was already a very successful writer at the time, having written extensively for TV shows like Alfred Hitchcock Presents and co-created Naked City and Route 66. Allan Silliphant was famous by association, a fact used by Savage to draw in potential investors.
The younger Silliphant brother had no idea that the family name was being used to influence potential investors. Savage reportedly offered many of the investors a small part in the film for a few hundred dollars each, in exchange for a part of the profits. Savage paid Allan Silliphant $1,500, according to comments by Silliphant when interviewed by director Pete Schuermann for The Creep Behind the Camera (aka Creep!) (2014), a docudrama film about the making of The Creeping Terror. In Harry Medved and Michael Medved's Son of Golden Turkey Awards, far less was implied by the authors. Forthwith, the 22-year-old Silliphant returned in three days with the original nine-page film treatment that he had "made up" face-to-face with Savage, based only on a vague earlier story idea. Later in the production there was conflict between writer and director, with Silliphant growing frustrated that Savage did not seem to share his vision that the story was "supposed" to be over the top.
Principal photography on location began in late 1962 but instead of shooting at scenic Lake Tahoe as Silliphant had intended, a muddy pond at Spahn Ranch in Simi Valley, California, had to do. When the creator of the special effects was not paid, he "stole" the original creature just a day before shooting, forcing Savage and his crew to put together a poorly constructed replica. In John Stanley’s Revenge of the Creature Features Movie Guide (1988), he described the creature as “...an elongated alien monster resembling a clumsy shag rug which devours people through a gaping maw, overturns cars and takes forever to shamble 10 feet!” With prolonged breaks as production difficulties were overcome, and new financing obtained, location shooting resumed in 1963, during spring and into hot summer months, while studio work continued at the Metropolitan International Pictures studio.
Silliphant saw that the direction the film was taking would harm his family, especially the reputation of half-brother Stirling, rather than enhance it, so he bowed out after the studio scenes were done. The production became a weekend affair for several more months, with Savage raising the money by selling small parts to star-struck plumbers, and others. Savage may also have checked into a motel with a silent picture-only Moviola to do a quick assembly of the film. There is only a limited amount of dialog in the film, because Savage supposedly shot scenes without regard to the professional quality of the sound, or even transferring it properly to 35mm mag stock. Having insufficient money to pay for basic sound transfers, Savage finally hired a local radio news reader to narrate the entire film in post-production, although some re-dubbing of characters does take place. The narrator speaks over much of the dialog in the film while long bouts devoid of dialog have no narration (similar in style to many of the educational films of the 1950s and 1960s).
Reportedly the original sound tracks were lost, although the film may have been shot without sound as a cost-saving measure, and that dubbing was to have taken place after production. Just before the film's release, Savage was repeatedly sued, and facing a possible indictment on charges of fraud, vanished. He was apparently never heard from again in the context of film production, and reportedly died of liver failure in 1975, aged 41. In 2009, his wife, Lois wrote a "tell-all" novel that featured her life with Savage, albeit using aliases.
With Savage disappearing, as the main financier, William Thourlby acquired the remaining film stock and had an edited version created in order to recoup some of his investment. The Creeping Terror would not be suitable for wide release and although, at best, it would have been relegated to drive-in theaters and second run showings, instead, it was sold to television in 1976 as part of a syndication package of films for local UHF channels. In 1994, The Creeping Terror was featured in episode #606 of Mystery Science Theatre 3000. The cast and crew (and later fans) of Mystery Science Theater 3000 were the film's most prominent critics. TV Guide called The Creeping Terror "pure camp" and said that it might be the second-worst horror film ever made, ahead of only Plan 9 from Outer Space.