Superman (Christopher Reeve) decides to rid the Earth of all nuclear weapons. After gathering them all into a giant net in space, he tosses it into the sun.
Lex Luthor (Gene Hackman) uses this to his advantage by designing his own evil super-villian. Using a strand of Superman's hair, he constructs a device which he attaches to a nuclear missle. The missle is lanched and Superman catches it and throws it into the sun. Luthor's creation, Nuclear Man, is born.
Superman and Nuclear Man fight and Superman is mortally injured. After being gone for a few days, we see Superman struggling for his life and lying in bed. He brings out the green crystal and we hear his mother's voice encouraging him to use it one more time to heal himself.
Superman returns and defeats Nuclear Man.
**On a brief side story, there is a moment when Superman kisses Lois (Margot Kidder)and she remembers who he his again (Referring to Superman II). Then he kisses her again and she forgets**