1934. Seventeen-year-old Cassandra (ROMOLA GARAI) lives in a dilapidated castle in Suffolk with her eccentric family. Her father, Mortmain (BILL NIGHY), is a reclusive writer who has been suffering from writer's block ever since the publication of his highly-acclaimed debut novel twenty years previously. His wife died some years ago and Mortmain is now married to Topaz, a beautiful and bohemian former artists' model several years younger than him. Cassandra has a younger brother, Thomas (JOE SOWERBUTTS), and an older sister, Rose (ROSE BYRNE), the beauty of the family who is desperate to escape their impoverished circumstances.