The film follows 17-year-old Cassandra Mortmain, and her eccentric family, struggling to survive in genteel poverty in a decaying English castle. The characters include her father, a writer who hasn't written anything in the 12 years since the spectacular success of his first novel; her older sister Rose, who rails against their fate and hopes to marry for money; and their bohemian stepmother, Topaz, an ex-model still apt to sun-bathe in the nude. The possibility of salvation seems to loom in the form of their wealthy American landlord Simon Cotton and his brother Neil. Although Simon initially spurns her, Rose is determined to make him fall in love with her and succeeds. A wedding is arranged and Cassandra appears to be left on the sidelines. Cassandra is confused not only by her feelings for the Cottons but also for Stephen Colley. Stephen is the incredibly attractive son of the Mortmains' former chef who acts as a handyman to the family and is deeply in love with Cassandra. But events spiral out of control, and before the summer ends many expectations will have been overturned.
Romola Garai as Cassandra Mortmain
Henry Thomas as Simon Cotton
Rose Byrne as Rose Mortmain
Bill Nighy as James Mortmain
Tara Fitzgerald as Topaz Mortmain
Marc Blucas as Neil Cotton
Henry Cavill as Stephen Colley
Sinéad Cusack as Elspeth Cotton
Joe Sowerbutts as Thomas Mortmain
James Faulkner as Aubrey Fox-Cotton
Sarah Woodward as Leda Fox-Cotton
David Bamber as the Vicar
Helena Little as Mother
based on the 1948 novel of the same name by Dodie Smith