Though theirs is a marriage of true equals, when Sherlock Holmes summons his wife and partner Mary Russell to the eerie scene of his most celebrated case, she abandons her Oxford studies to aid his investigation. But this time, on Dartmoor, there is more to the matter than a phantom hound. Sightings of a spectral coach carrying a long-dead noblewoman over the moonlit moor have heralded a mysterious death, the corpse surrounded by oversize paw prints. Here on this wild and foreboding moor, Russell and Holmes embark on a quest with few clues save a fanatic anthropologist, an ancestral portrait, a moorland witch, and a lowly- but most revealing- hedgehog. As Holmes and Russell anticipate, a rational explanation lies beneath the supernatural events- but one darker than they could have imagined. And one that could end their lives in this harsh and desolate land.