Nova is a parallel version of Superman from Earth-178.
While exploring a strange dimension, Superman was exposed to a peculiar substance that permanently destroyed his powers.
Forced to live as Clark Kent, he eked out a dreary existence, until one day he attended a charity ball where Green Arrow and Speedy were putting on a demonstration. Inspired by their example, as well as that of Batman and Robin, he set forth to create a non-powered superheroic identity: Nova.
Fashioning a unbreakable cape that let him glide on the wind, and within which he'd incorporated numerous gadgets, Kent spent a week training in secret on an abandoned movie lot in Gotham. Being mistaken for a prowler led to a brief (and losing) confrontation with Batman, who wished the nascent hero luck, but privately expressed his doubts to Robin.
A few days later, Nova's inaugural run against a group of thugs ended with him being beaten severely and kidnapped, in part because he kept fighting as if he were still super-strong and invulnerable.
Awakening unmasked in the presence of their boss Mr. Socrates, the former Superman was implanted with a (slightly glitchy) device that would allow the criminal mastermind to monitor him and control his actions from a distance.
Kent was made to travel to Gotham City, where "Nova" began a crime rampage that led Batman to a half-finished building. Kent, having changed into his old costume, explained that after Batman was dead, the police would be looking for Nova and he'd get off scot-free. A fight among the girders led to Batman knocking him unconscious and taking him back to the Batcave, where they found the control device.
Kent awakened, breaking his restraints and stealing the Batmobile, and Batman revealed that he'd weakened the straps so that they could pursue Kent in the Batcopter and see who was pulling his strings.
During the chase, the controlling device faltered for a few moments, and Kent, having realized that high-frequency radio waves might interfere with its functioning, managed to get to Jimmy Olsen, who was covering a story nearby. Jimmy's signal watch jammed the device long enough for Batman and Robin to cover it with a lead collar.
Meanwhile, Socrates and his gang had used the signal from the control device to pinpoint and infiltrate the Batcave, where they laid an explosive trap for Batman and Robin, only to find that the Dynamic Duo and returned much earlier than expected.
Unable to control Superman and with his thugs beaten, Socrates panicked and fled into his own trap, dying instantly. His thugs would have their memory of Batman's identity wiped by Green Lantern.
In the end, Kent lamented his failed career as Nova, and prepared to retire for good, but Batman and Robin offered to train him themselves, with the outcome left to the reader to decide.