A young man visits his fiancé’s estate to discover that her wheelchair-bound scientist father has discovered a meteorite that emits mutating radiation rays that have turned the plants in his greenhouse to giants. When his own wife falls victim to this mysterious power, the old man takes it upon himself to destroy the glowing object with disastrous results.

Professor “Johnny Longbow” Salina, a man who really knows his stews, introduces Paul Carlson to the practical-joking Kathy Nolan. Paul and Kathy seem to hit it off rather well but, during a meteor storm, a meteorite fragment strikes Paul, burying itself deep in his skull, which has the unpleasant side-effect of causing Paul to mutate into a giant reptilian monster at night and go on murderous rampages. It turns out that this sort of thing has happened before, when Professor Salina rediscovers ancient Native American paintings detailing a similar event many centuries ago. Kathy, however, still loves Paul, and tries to save him.