As the townsfolk of the Welsh valley town of Llanelen settle in for the snowiest winter in 25 years, an American stranger arrives. Harry Saunders charms the ladies and one in particular – Evelyn Lloyd, the town's former post mistress who was left comfortably off after the death of her husband. Harry convinces Mrs. Lloyd to invest money with him. Then he goes missing, as does her money. His body is soon discovered outside the walls of Conwy Castle, a letter opener belonging to Mrs. Lloyd in his back.

Penny Brannigan is busy with the grand opening of her new spa, but that doesn't stop Mrs. Lloyd from desperately seeking her help to prove her innocence.