The film follows 17-year-old Cassandra Mortain (Romala 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 has written a word in 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.