Based on the novel by Dodie Smith (101 Dalmatians), director Tim Fywell's comic romance follows 17-year-old Cassandra Mortmain (Romola Garai) and her quirky family as they attempt to make the best of their meager existence in a crumbling English castle. While her father (Bill Nighy) has been struggling for over a decade to repeat the success of his debut novel, her beautiful sister Rose (Rose Byrne) frequently voices her displeasure with their current situation, and nudist stepmother Topaz (Tara Fitzgerald) proves little help at much of anything. The arrival of American landlord Simon Cotton (Henry Thomas) and his brother Neil (Marc Blucas) provides a glimmer of hope as the initially repelled Rose soon takes a liking to Simon and the two arrange to marry. Lost in the chaotic shuffle of marriage plans and increasingly complicated relationships, the hapless Cassandra soon begins to blossom into womanhood as she experiences aspects of life that were heretofore unknown to her.