A SUNDAY TIMES BESTSELLERA WATERSTONES BOOK OF THE MONTHA BBC RADIO 4 BOOK OF THE WEEKAs winter comes and the hours of darkness overtake the light, we seek out warmth, good food, and good company. But beneath the jollity and bright enchantment of the festive season, there lurks a darker mood - one that has found expression over the centuries in a host of strange and unsettling traditions and lore.