The year is 1901, and Ada Byrd - spinster, schoolmarm, amateur naturalist - accepts a teaching post in isolated Lowry Bridge, grateful for the chance to re-establish herself where no one knows her secrets. She develops friendships with her neighbours, explores the woods with her students, and begins to see a future in this tiny farming community. Her past - riddled with grief and shame - has never seemed so far away. But then, Ada begins to witness strange and grisly phenomena: a swarm of dying crickets, a self-mutilating rabbit, a malformed faun. She soon believes that something old and beastly - which she calls Grey Dog - is behind these visceral offerings, which both beckon and repel her. As her confusion deepens, her grip on what is real, what is delusion, and what is traumatic memory loosens, and Ada takes on the wildness of the woods, behaving erratically and pushing her newfound friends away. In the end, she is left with one question: What is the real horror? The Grey Dog, the uncontainable power of female rage, or Ada herself?