Trixie Belden #11 - The Mystery at Bob-White Cave - 1963
The gang heads to Uncle Andrew's fishing lodge in the Ozarks. Trixie gets everyone to go spelunking in hopes of finding some cave fish and winning $500 for charity. But it looks like there's competition from an Englishman, plus Trixie doesn't quite trust their guide. Throw in a "ghost" cabin and you've got another mystery for Trixie to solve.