When they take lodgings in Colchester, rumours reach them from further up the estuary that the mythical Essex Serpent, once said to roam the marshes claiming human lives, has returned to the coastal parish of Aldwinter. Cora, a keen amateur naturalist with no patience for religion or superstition, is immediately enthralled, convinced that what the local people think is a magical beast may be a previously undiscovered species. As she sets out on its trail, she is introduced to William Ransome, Aldwinter's vicar.
Like Cora, Will is deeply suspicious of the rumours, but he thinks they are founded on moral panic, a flight from real faith. As he tries to calm his parishioners, he and Cora strike up an intense relationship, and although they agree on absolutely nothing, they find themselves inexorably drawn together and torn apart, eventually changing each other's lives in ways entirely unexpected.
Told with exquisite grace and intelligence, this novel is most of all a celebration of love, and the many different guises it can take.