Clark stared at the lead box in the middle of the coffee table. Sealed shut by several locks, it held the only piece of kryptonite on Earth. Clark, as Superboy, had seized it from Luthor after Lex trapped Superboy in a mine shaft with the deadly rock. Luthor triggered an explosion hoping to bury Superboy and the kryptonite under tons of debris. Fortunately for Superboy, the explosion caused the side of the mountain to collapse - trapping Luthor too. In the end Luthor decided dying along with Superboy was not part of the plan and he worked with the injured superhero to escape the mine shaft. Superboy recovered and took possession of the kryptonite while Luthor was tried and sentenced to five years in jail. Unfortunately, just after Clark's move to Metropolis, he learned that Luthor had been granted early parole for good behavior. Good behavior – yeah right! If that wasn't enough, Luthor was moving to Metropolis – to "do good deeds." So he told the parole board. Coming just weeks after Superboy - now Superman - had made his Metropolis debut, Lex's intentions were obvious to Clark but apparently not to the wizards of smart on the parole board.
Luthor aside, kryptonite was a mystery. The glowing rock should not exist on Earth. Professor Peterson had determined it to be a small piece of a long extinct planet - Krypton. The Professor was perplexed. Krypton had been destroyed by a super-nova which sent pieces of Krypton and all nearby celestial bodies in a direction opposite that of the Milky Way Galaxy. Compounding the mystery was the meteor's devastating effect on Superboy while it had no affect on other humans. Frustrated, Peterson had asked Superboy "what is the connection between you and this rock?". The Professor hadn't really expected an answer and Superboy didn't really give him one – other than to say "Beats me."
However it got to Earth and whatever its connection to Superboy, kryptonite was lethal to the young hero. Weakening him immediately, all but paralyzing him in a matter of minutes, the radiation was so potent that Professor Peterson warned Superboy it could kill him in less than an hour. Peterson had tested the kryptonite with Superboy present using a laser device to aim a small beam of the green radiation at Superboy's forearm. Superboy immediately screamed in agony and Peterson quickly shut down the laser. The area on Superboy's forearm where the beam was targeted was blistered and had a yellow/green discoloration. The Professor was able to get several samples of Superboy's skin before the area healed with no sign of a scar. Despite filtering the radiation and reducing its potency a thousand fold, the kryptonite beam had hurt the Boy of Steel. The two decided not to expose Superboy to more radiation. Not only was it too painful, but both worried that there could be permanent damage from repeated exposures - perhaps compromising his powers. Or inducing cancer in coming years just as repeated human exposure to radiation can lead to cancer.
Kryptonite or not, Luthor was brilliant and seemed destined to become ...
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This story loosely flows from The Adventures of Superboy TV universe. Clark Kent makes his debut as Superboy while in his freshman year at Shuster University. Lex Luthor, coincidentally, attends the same university. They first meet and tangle in their freshman year. Graduating from college Clark moves to Metropolis to work for Planet Global Communications and to become Superman. The story takes place during Clark's first months in Metropolis. In this universe Superman's costume is classic - bright, vivid colors and the dreaded trunks. It is the costume worn by Gerard Christopher in The Adventures of Superboy series - more than a few of us consider it to be the best ever live-action Superman suit. The mine incident comes from the Mine Games episode and the hypersonic gun is first seen in the episode Luthor Unleashed.