Remember the time Superman destroyed the Earth by accident and they never let him live it down? No? Then there must be some kind of Silver Age shenanigans at work. It's a lazy day in the Fortress of Solitude, with Superman, Supergirl and Krypto just chillin', when a plane decides it's going to land on the ice outside. Well, that must be prevented on the off chance someone discovers the location of the Fortress! That impregnable mountain HQ with the giant key only a Kryptonian can lift, yeah? Quick, give me all your capes!
Meanwhile, in Superman's boyhood... Superboy is turned intangible and invisible by the Phantom Zone projector and Krypto flies right through him.