Nancy is going on a trip with her friends, George Fayne and Bess Marvin, to Mirror Bay. There are multiple mysteries going on in this place. The first mystery is when people see a woman gliding across the bay at night. The second is a green man that frightens people of the mountain nearby. The third is a missing child's carriage that was lost in the bay. Yet the green man and the carriage mysteries seem tied together. Could it be that the two are not unrelated?