a male voice rasps on the telephone. Despite the mysterious warning, the teenage detective and a group of friends start out on a ghost-hunting expedition to investigate five places reputed to be haunted. Danger strikes at once when Nancy tries to overtake the canoe that paddles itself on Lake Sevanee. Thrills and chills mount as the ghost hunters pursue a phantom horse and ghost rider racing across the field that surrounds the Red Barn Guesthouse. During these happenings and other weird events Nancy finds herself pitted against a dangerous adversary, clever enough to operate invisibly.