Cornwall, 1844. On a lonely moorland farm not far from Jamaica Inn, farmhand Shilly finds love in the arms of Charlotte Dymond. But Charlotte has many secrets, possessing powers that cause both good and ill. When she's found on the moor with her throat cut, Shilly is determined to find out who is responsible, and so is the stranger calling himself Mr Williams who asks for Shilly's help. Mr Williams has secrets too, and Shilly is thrown into the bewildering new world of modern detection.