McCoy Saderly and his two best friends are preparing for a three-day hike in the Mark Twain National Forest when a thug breaks into a local candy store, attacks the owner, and snatches a mysterious black pouch from behind a wall. Now only one question remains: What is so valuable that someone would hide it in a store in Sherwood, Missouri?
As McCoy and his buddies make use of their status as honorary FBI agents once again, the mystery winds its way through the candy store, the lab of a zany scientist, the forest, and the seemingly long-forgotten annals of a historical community. When the mysterious pouch containing an odd pennylike coin with a smudgy residue is secretly put back, McCoy's curiosity gets the best of him. Along with a new friend named Drue, who stirs up the mystery even more, the gang pursues the truth while a hidden foe tracks their every move. Will FBI agent Grady Frost get involved in time, or will the treasure hunt to the top of Bell Mountain be stopped before the mystery is solved?