Sunblock can't save you from the solar-powered monster in this sci-fi cult item. Dr. Gilbert McKenna (Robert Clarke) is a research scientist who is exposed to dangerously radioactive materials during a visit to an atomic power plant. The radiation causes McKenna to mutate into a strange and murderous half-man, half-reptile when he comes into contact with the rays of the sun. The isotopes also have another effect on him; he begins to forget about his loyal girlfriend Ann Russell (Patricia Manning) and starts taking up with blonde bombshell Trudy Osborne (Nan Peterson), who brings out the beast in him as surely as the sun. The Hideous Sun Demon was co-produced, co-written, and co-directed by leading man Robert Clarke; it was his first and last effort as a writer and director, though he was to remain active as an actor for another 30 years. In 1983, a group of comedians re-edited the film and dubbed in a new soundtrack; the results were released as What's Up, Hideous Sun Demon?