A bit of an odd one, this issue features a team-up of Superman and the Challengers of the Unknown. Kirby pencils the cover and first 2 pages, then Alex Toth pencils a 7 page flashback and Kirby is back for the remaining 15 pages. Bob Rozakis writes and Greg Theakston inks the whole thing. I think the Toth sequence was originally supposed to be a chapter in the Rozakis/Toth Challengers series that briefly ran in ADVENTURE COMICS DIGEST, modified here to lead in to the crossover with Superman.
Anyway, this story features the Challengers coming to the Daily Planet looking for Superman. Clark Kent comes in, and they tell their story about how they tried to save a man on a ledge, and found a card with what they recognized as Kryptonian symbols. Superman uses his old mind-prober to recall when he saw that symbol as an infant, as a mind-control device used by Zo-Mar, a criminal who was exiled to space before Jor-El discovered the Phantom Zone.
With the Challengers, Superman finds Zo-Mar and they're eventually able to defeat him using such Superman concepts of the period as super-ventriloquism. Zo-Mar is sent off to the Phantom Zone, where we get a teaser for a sequel that I'm not sure was ever published as Superman's history was scrubed clean soon after.
A bit of a footnote in Kirby's career, but it was interesting to see him draw the Challengers one last time, and Superman without being redrawn. It's kind of disapointing that, even though he's mentioned a few times, Jimmy Olsen doesn't show up in the actual story.