Market Day is buzzing at Bellwether Creek Elementary, and Gid Ralston is certain his team has built the best business in town. With Tess counting cash, June recording sales, Bram demonstrating inventions, and Axo watching from Gid's bicycle display, the Bellwether Tech Cart is a runaway success. But when the market closes, something doesn't add up: their records say they earned seventy-four dollars, while the cash box holds only forty-nine. Suddenly, a school fair becomes a mystery. As suspicion falls on Bram, Gid and his friends must follow the clues, check the numbers, and discover where the missing twenty-five dollars went.