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. Her father (Bill Nighy) is desperate to repeat the spectacular success of his first novel, but hasn't written a word for 12 years; her exquisite sister Rose (Rose Byrne) can only rail against their fate, and their Bohemian step-mother Topaz (Tara FitzGerald) is a nudist and 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.