The moral of this film is don't drink and do science at the same time! Alas, Gilbert McKenna had to learn this the hard way. He went to work at the radioactive isotope lab with a severe hangover, and, surprise, surprise, there was an accident. Poor Gil went and got himself exposed to a new type of isotope he and his colleagues were working on. He's rushed to the emergency room, but shows no immediate signs of injury. No burns on anything, thoroughly stumping the ER doctor. Ann Russell and Frederick Buckell, his aforementioned colleagues, are concerned about what kind of side effects exposure to their pet isotope may have.
We get to find out soon enough. While convalescing outside in the sun, Gil starts feeling a little... weird. He freaks the hell out and thoroughly terrifies some poor old biddy who'd joined him, and, realizing that he turns into a hideous sun demon when exposed to direct sunlight, he flees home and shacks up with lounge singer Trudy Osborne, in whose home he decides to hide. But, unfortunately for all concerned, Trudy has a jealous boyfriend, and said jealous boyfriend has a gun (whether it's a Colt or a Luger the editor apparently couldn't decide). He forces the competition outside at gunpoint, whereupon Gil promptly turns into the hideous sun demon and murders him (and of course he doesn't think of actually using
the gun to defend himself), then escapes.
Lt. Peterson of the police and his men are soon hot on poor Gil's trail, despite the objections of Ann, Fred and their friend Dr. Hoffman, who may or may not be German. His accent can't decide. Ever the by-the-book cop (i.e. a talking plank of wood without a personality), Peterson is hellbent on hunting and killing Gilbert, sun demon or not. The thoroughly goofy pursuit sees Gil the monster kill some cops before one particularly tough officer chases him to the top of an oil tank in the middle of nowhere, where the hideous sun demon finally meets his ultimate foe: bullets and gravity.
Pure schlock, but I loved it.