The film follows 17-year-old Cassandra Mortmain (Romola Garai), and the fortunes of her eccentric family, struggling to survive in a decaying English castle. The characters include: Cassandra's father (Bill Nighy), a writer who hasn't written anything in the twelve years since the spectacular success of his first novel; her exquisite sister Rose (Rose Byrne) who can only rail against their fate; and their Bohemian stepmother, Topaz (Tara Fitzgerald), a nudist who is no help at all. Salvation comes in the form of their American landlord Simon Cotton (Henry Thomas) and his brother Neil (Marc Blucas). Although initially repelled by Simon, Rose is determined to make him fall in love with her and succeeds. A wedding is arranged and Cassandra is left on the sidelines as everyone around her is drawn into a maelstrom of interconnected relationships. But events spiral out of control, and before the summer ends she will experience frustrated desire, first love, and a broken heart.