Maxie and 99 in the Florida swamps.
A natural region of flooded grasslands in the southern portion of the U.S. state of Florida [Wikipedia].
The area is supposedly the swampy origin of a certain root which is the secret of Doctor Egghead's non-elastic rubber band.
Kidnapped by C.I.N., Egghead is forced to reveal this secret and is taken there forthwith so that C.I.N. can take possession of it.
Egghead is rescued by Smart and 99 but upon returning to CONTROL it is revealed that the professor is in fact the Chief's Uncle Ed and the real Egghead is safe and sound elsewhere, the true secret remaining untold.
[Comic Strip Story #7 (Unofficial title: "Doctor Egghead").]