Gillian's Marsh, 1866. The foul and treacherous wetlands where a young woman, Louella Lee, ends up after escaping the horrors of her puritanical home in the town of Gillianswick. Collapsing in the black woods near the marsh, she is found by Red, a loner woodsman, and their rendezvous sets a nightmarish wheel into motion. Whilst their unorthodox relationship blossoms, stakes are burning in Gillianswick after a series of strange disappearances. Convinced that the town is in the grip of black magic and deviltry, overzealous Cyrus Reiterman initiates a merciless witch-hunt that eventually draws him to the betraying bog, where baleful forces await...