Superman's character is seriously tested in ethical and physical battle with the demon prince of the netherworld. The demon is called C.W. Saturn. (Hmm, CW... coincidence that the hell-spawned 'Smallville' would later run for an eternity on the CW???)
Also, it's got time traveling historians! Specifically, Kristin Wells, gutsy 29th Century scholar studying Superman while disguised as Lois Lane's anachronism-spewing assistant. (The character would briefly appear in the comics as Superwoman, an apparent darling of Maggin's. She's pre-Crisis, and vanished from comics so completely afterward that I've never heard of her till this week.)
Time travelers AND demons? What the what? The unholy marriage of sf and fantasy works beautifully. It's a high compliment for me that this reminds me of Douglas Adams' stuff; off-the-rails impossible and still internally logical. A sweet thing to behold.
Absolutely more fun than 'Downbelow Station', which won the Hugo Award for the year 1981.
So I hope DC paid the author well, or that it satisfied him to write it, or both. Elliot S! Maggin deserves to be remembered until 2857 and beyond.