The hero is contaminated by a radioactive cloud, and begins gradually shrinking. The film follows him as he gets smaller; for a time he finds some companionship with midgets, but continues to shrink; eventually reduced to living in a dolls-house. After nearly being killed by a cat, he winds up trapped in the basement and engaged in a life-and-death struggle with a spider. The camera work and effects for the shrinking hero are extremely well done, and with a great deal of imagination. (The drops of water dripping from the boiler near the end of the film were actually created using water filled condoms; the consuption of large numbers of these raised eyebrows amongst the film company's accountanta)
In the end, the hero accepts his continuing accelerating shrinkage, and looks forward to see what waits for him in the realsm of the ever smaller.