Set in Victorian England, the series follows Cora Seaborne, a recently widowed woman who moves from London to the small village of Aldwinter in Essex. Cora is intrigued by a local superstition that a mythical creature known as the Essex Serpent has returned to the area, and she becomes determined to investigate the scientific possibility of its existence. Her arrival sparks both curiosity and fear among the villagers, who are deeply divided between religious faith and scientific inquiry. As Cora delves deeper into the mystery, she forms an unlikely bond with the local vicar, William Ransome, who is a man of science and faith struggling to maintain order in his parish. Their relationship is tested by their conflicting worldviews and the growing hysteria surrounding the creature. The series explores themes of obsession, the tension between religion and science, and the complexities of human connection in a rapidly changing society.