During the midsummer of 1752, following a desperate summons from her mother, Tabitha Hart departs London for her home village of Netherlea - only to discover that her mother has drowned. Determined to discover the truth about the Widow Hart's death, Tabitha consults her almanack and uncovers a series of cryptic notes describing her mother's terror of someone she names only as 'D'. Teaming up with young writer Nat Starling, Tabitha begins a race against time to unmask 'D' before more deaths follow. But as the summer draws to a close and the snow sets in, cutting off Netherlea from the outside world, Tabitha and Nat are forced to face the darkest hours of their lives.