It is 1910 and to ten-year-old Oskar Grunewald, the Melville family is impossibly, incomprehensibly glamorous. Born into privilege, their certainties are as unshakeable as the walls of their Victorian castle. It is a world to which Oskar, mathematics prodigy and son of a penniless German composer, has no wish to belong. But when Theo Melville is killed in the Great War, shattering his family's lives, Oskar finds himself drawn reluctantly into the gaping hole his death has left behind. As Theo's two sisters struggle to forge their paths in a world that no longer plays by the old rules, Oskar's life becomes entwined with theirs in a way that will change all of their futures.