Suffolk, 1937. As the county suffers the worst heatwave in living memory, at Snare House preparations for a party are in full swing. The Winthers' only daughter, Joanie, is returning from a summer in Europe, a flying visit before she takes up a place at university. Only Margaret, long-time ward of the family and Joanie's closest friend, knows the truth: Joanie won't go to Oxford. Because the night before she left, they told each other how they really felt - and Joanie won't want to be anywhere but with Margaret, ever again. But when Joanie's father discovers their intentions, Margaret's plans are turned upside down. Exiled to a tumbledown lodge in the woods with her estranged father and his colony of magpies, she finds herself becoming wild: her dreams vivid and terrifying, waking with dirt on the soles of her feet. As the heatwave refuses to break, Margaret must choose whether to give in to her new, dark impulses - the same ones she is beginning to suspect killed her mother - in a bid to get what she wants.