When a family friend, Grace, opens a sailing club on Lake Champlain at the former site of the Gemstone Islands Resort, Nancy, Bess, and George are invited to enjoy a few days of boating before the club's official grand opening. But when they arrive, they learn there have been some strange things happening on the property, from missing items to holes dug all over the yard. Is someone trying to sabotage the club, and could it have anything to do with the fire that destroyed the old resort twenty years ago?

As Nancy tries to pry information from the tight-lipped locals, all clues lead back to Captain Richard Stone, the enigmatic Revolutionary War-era pirate whose tavern once stood on the same site as the resort and sailing club. Legend has it that Captain Stone's ghost still haunts the property, guarding the treasure he buried there. But it isn't a ghost that punches a hole in Nancy's sailboat, leaving her and the girls to sink in the middle of the lake when an unexpected summer storm rolls in.

Unraveling the mystery of Captain Stone's treasure will be the key to finding out who's been sabotaging Grace's club. But first, Nancy and her friends will have to make it back to shore in one piece...