The Haunted Bridge (Nancy Drew, Book 15) by Carolyn Keene

Mr. Drew is on the trail of an international ring of jewel thieves and asks Nancy to assist him. The trail leads to a summer resort area. Before Nancy has a chance to start work on her father’s case, a golf caddy tells her a frightening tale--in the dense woods nearby is an old wooden footbridge guarded by a ghost! Intrigued by the caddy’s story, Nancy decides to investigate. Several riddles confront the young detective as she attempts to solve the mystery of the haunted bridge and track down a woman suspected of being a key member of the gang of jewel thieves.