Challengers of the Unknown Novel...literally
The Challengers of the Unknown are relatively...well...unknown to probably all non comic book readers and even most casual comic book readers.
Spawned from the Silver Age of comic book history (debuting in Showcase #6 - Feb. 1957), Kyle "Ace" Morgan, Matthew "Red" Ryan, Leslie "Rocky" Davis, Walter Mark "Prof" Haley and later (and included in this novel) June Robbins are a group of adventurers who formed after the original four (Ace, Red, Rocky and Prof) survived a plane crash that should have spelled certain doom; thereby devoting their lives to doing good in the face of certain death (since, what the hell, they are living on borrowed time anyways.)
This novel, penned by Ron Goulart, is about a lake monster in South America wrecking an American Oil company's interests; apparently Scooby and the gang were busy on another case, so the Challengers of the Unknown are called in to save the day!
I'm only a couple chapters into it so far, but I was super excited to find this obscure publication and couldn't wait to dive right in. Aw yeah flea market!