Scientists turn Lucy Lane's new boyfriend, a loser with a rap sheet, into a cyborg criminal. This looks like a job for Superman - except the cyborg is powered by Kryptonite!
Lois' sister Lucy moves back into the town with her new boyfriend Johnny Corben, who Lois does not like and tries to convince Lucy that he is no good for her and only using her, leading them to fight.
Meanwhile, two scientists Emmet and Rollie Vale create robots that they use to rob jewelries. After Johnny gets shot by police during a robbery, the two scientists take his head and transform him into a cyborg that is powered by Kryptonite.
Under the name Metallo, Johnny uses his new body to steal money from ATMs and also tries to defeat Superman. On their first confrontation, Superman is defeated due to the Johnny's hidden power source of Kryptonite. Superman realises the existence of it and the next time they meet, he knows how to fight Johnny without him getting affected by the dangerous substance. Johnny gets defeated while Emmet gets arrested and Rollie runs away with the Kryptonite.
- Scott Valentine as Johnny Corben/Metallo
- Roxana Zal as Lucy Lane
- John Rubinstein as Emmet Vale
- Christian Clemenson as Rollie Vale
- Louis Mustillo as Detective
- Dee Dee Rescher as Mrs. Vale
- Mary Pat Gleason as Postal Inspector