Mystery up the winding stair

A boy, Harry, is staying with his grandfather in his grandfather's big mansion while his parents are away. The mansion is a fascinating place, and it even has its own small museum dedicated to life in early America, complete with a small log cabin exhibit. However, the mansion is also a little lonely with just the boy and his grandfather, so the grandfather invites Harry's cousins to come for a visit and gives the children a task: to find a missing treasure that the grandfather himself hid many years ago. The grandfather has forgotten where he hid a set of spoons made by Paul Revere and a diamond. Soon, a blizzard traps the family in the mansion, and they realize that they are not alone. Someone else is hiding in the house, and he wants the treasure, too!