Everybody loves Mr. Roper. He gives kids free candy or ice cream when their parents shop at his grocery store. So when he's accused of selling stolen oysters, Mr. Merlin's Third-Grade Detectives don't believe it. But can they prove it? Mr. Merlin's secret codes have the Detectives looking for clues at the beach, at rival oyster farms, and even in a garbage truck — yuck! It turns out pearls aren't the only valuable thing you can get from oysters — you can also get evidence to help solve a baffling mystery!