The Case of the Midnight Stranger (formerly Reflecto Man) (Pony Investigators Book 3)

Astride their ponies, Ginger and Oreo, twelve year olds, Amy Jo and Becky,
solve mysteries and crimes in the small town of Bedford. In The Case of the Midnight Stranger, a mysterious arrival wearing reflective sunglasses has moved into the old Johnson place. From the widow's walk built on top of the house, he signals someone at the quarry. The Pony Investigators are convinced that he has teamed up with a man they suspect is a criminal. When they approach Chief Higgins with their suspicions, he is strangely reluctant to do anything about it. Against the chief's strict orders, Amy Jo and Becky return to the quarry where danger awaits them.