In the story, Jor-El, Lara, and Kal-El survive the destruction of Krypton. Brainiac, who's a good guy in this story, shrinks Kryptonopolis instead of Kandor, in order to save it, but is unable to do the same for the rest of the planet:
Eventually Brainiac finds the expanding element, but before he can use it his ship is hit by a meteor and crashes on Earth. Fortunately, he had transferred a little of the element to Jor-El, who realizes he can enlarge one person to send out to the planet to become its protector.
And so, Kryptonopolis has a contest to see who will become Superman:
The contestants are eliminated one by one, until only Kal and Knor are left. Note in particular that this segment echoes the origin of Wonder Woman, who was selected to take Steve Trevor back to the USA in a very similar competition. In the finale, contrary to the cover scene, both men have to battle robots:
Comments: Overall the story seems a little light, with few of the twists and turns that usually took place under Weisinger's editorship.
As noted earlier, there is not a lot of hype about the 200th issue, unlike the forthcoming Batman #200, which included a long conversation between two Bat-fans, a reprint of the first page from Detective #27 and a cover hyping the "200th Smash Issue". There is some mention of it in the letters page: