An ominous cover for the story by Cary Bates, Curt Swan and Jack Abel in Superman 213 (Jan. 69).
It’s been quite a while since Lex Luthor appeared in these pages, but he returns in this story, obsessed with a mysterious vault that Superman has created, which can only be opened after his death. Luthor drills from underground to reach the vault, and uses a shrink ray he stole from Brainiac to remove it completely and bring it back to his headquarters.
But even as all this is going on, the story lets the reader in to the fact that it is some sort of hoax on Superman’s part, though the nature of it is unclear.
Luthor then captures and kills Superman, exposing him to kryptonite. But Jimmy Olsen and Supergirl are on hand to quickly revive the hero.
Even with Superman dead, Luthor has great trouble opening the vault. He finally succeeds, only to find Superman inside!
Superman had been trapped in the vault the whole time, sealed there magically by Mordru, an enemy of the Legion of Super-Heroes. The kryptonite poisoned Superman was really Brainiac 5, and the entire scheme a plan to have Luthor save Superman, without any idea what he was really doing.