Monster A Go-Go, (also released as Terror at Halfday) is a 1965 science fiction horror film directed by Bill Rebane and Herschell Gordon Lewis (who remained uncredited in association with this film).
The film had an unusual production history. Director Rebane ran out of money while making the film. Lewis, who needed a second film to show with his own feature, Moonshine Mountain, bought the film, added a few extra scenes and some dialogue, and then released it, creating an odd, disjointed film with little continuity. Rebane had abandoned the film in 1961; Lewis did not finish the film until 1965 and so was unable to gather all of the original cast, resulting in almost half the characters disappearing midway through the film to be replaced by other characters who fill most of the same roles. One of the actors Lewis was able to get back had dramatically changed his look in the intervening years, necessitating his playing the brother of the original character. The plot concerns an American astronaut, Frank Douglas, who mysteriously disappears from his spacecraft as it parachutes to Earth. The vanished astronaut is apparently replaced by or turned into a large, radioactive, humanoid monster. A team of scientists and military men attempt to capture the monster — and at one point succeed, only to have him escape again. Neither the capture nor the escape are ever shown, simply mentioned by the narrator. The website The Agony Booth recaps the perplexing storyline by re-assembling the revealed plot details (as of about an hour through the film) in chronological order of occurrence within the fictional world:
An astronaut is about to be sent up into space, and is given regular doses of "Radiation Repellent" for a while before the launch. For no particular reason, just prior to the launch, the astronaut's doctor switches to a totally different Radiation Repellent which hasn't been tested as much. And, naturally, he does this without telling any of his superiors. And, well, the test that they did conduct resulted in an animal doubling in size, right before that animal died. As expected with these kind of results, they not only gave the new repellent to the astronaut, but doubled his dosage. So, the astronaut's capsule crashes in an empty field The astronaut, thanks to the untested repellent, is now freakishly huge and killing random people. Until, that is, one scientist locks him up in a storeroom for eight weeks and gives him doses of an antidote. And, again, he does this without telling any of his superiors. At the end of the film, the scientists receive a telegram stating that Douglas is in fact alive and well, having been rescued in the North Atlantic. The narrator brazenly claims that there was never a monster in the first place:
As if a switch had been turned, as if an eye had been blinked, as if some phantom force in the universe had made a move eons beyond our comprehension, suddenly, there was no trail! There was no giant, no monster, no thing called "Douglas" to be followed. There was nothing in the tunnel but the puzzled men of courage, who suddenly found themselves alone with shadows and darkness! With the telegram, one cloud lifts, and another descends. Astronaut Frank Douglas, rescued, alive, well, and of normal size, some eight thousand miles away in a lifeboat, with no memory of where he has been, or how he was separated from his capsule! Then who, or what, has landed here? Is it here yet? Or has the cosmic switch been pulled? Case in point: The line between science fiction and science fact is microscopically thin! You have witnessed the line being shaved even thinner! But is the menace with us? Or is the monster gone? — closing narration
MONSTER A GO GO
BILL REBANE (1965)