Stakeout at the Stables

Starbright Stables riders Bess, Dot, and Lily want to compete in a new type of riding. It involves riding their horses through different obstacles. They build and gather what they need, from poles to gates and barrels. But then the obstacles start disappearing, only to appear again later! The girls set out to solve the mystery. They plan to camp overnight and keep their eyes glued to their equipment. What will they discover on their stable stakeout?