While working for his father at the Old Cooper Place, Billy discovers there's more to the property than just a rundown house, dilapidated garden shed, creepy cellar, and overgrown backyard. Rolling his rock-filled wheelbarrow over a small hole in the ground, it sinks into a much larger hole, crashing upon a macabre discovery that uncovers a myriad of clues pertaining to an ancient local mystery and possible treasure. But Billy wants to solve the puzzle on his own and encounters a number of obstacles as he strives to keep his newfound discoveries from his dad and nosy best friend, Jackie. The difficulties mount when Billy's band of friends decide to build a fort near the Old Cooper Place in a large tree overlooking the freeway that becomes front-row seats to a sinister caper, putting Billy in even greater danger than he or his friends ever could have imagined.