High up in the French Alps, the inhabitants of a small mountain village are busy preparing for Christmas. The toymaker Cornusse is occupied making presents for the children of the village, unaware that his beautiful young daughter, Catherine, is being courted by a mysterious baron. Having recently returned to the village after an absence of several years, the baron lives alone in his chateau and refuses to see anyone, until Catherine visits him out of pity. On Christmas Eve, the baron fails to keep a dinner date with Catherine, at the same time that a priceless diamond is stolen from the church. A short while later, two children from the village discover the body of Father Christmas lying dead on the snow-covered mountain slope. With the police prevented from arriving because of bad weather, the villagers attempt to resolve the mystery themselves and discover who killed Father Christmas...