Dragged off to spend Christmas in a rambling old house full of her new in-laws, amateur sleuth Verity Long is bored and isolated, but keen to make a good impression.

When Thor, the eight-year-old son of the house, tells her a fantastic tale, Verity thinks he's imagined it. But then, a mysterious woman is seen walking around the house on Christmas Eve, the family heirloom is stolen, and the children's tutor vanishes.

Verity's determination to solve the puzzle leads to a third disappearance. Now she must act fast, before something far more priceless than her relative's good opinion is lost to her - forever.