December 1st. Angie and her teenage son Rust prepare for Christmas, stringing fairy lights around their isolated home on the Somerset levels and decorating a tree with traditional ornaments. The first door of the advent calendar is opened, but the chocolate inside tastes off. Rust receives his first Christmas card; it's unsigned, and the message is 'pinch, punch. first of the month'. The robin chirruping on a bough in a snowy woodland picture looks like a nasty piece of work. The cards keep coming, one each day and each more sinister than the last, and a frightened Angie recalls 'The Cards' - a seasonal TV show from her childhood that featured similar happenings, and while she remembers it vividly, there is no evidence that it was ever broadcast.