"I Capture the Castle" is a novel by Dodie Smith that follows the life of Cassandra Mortmain, a teenage girl living in a crumbling castle in 1930s England. The story is narrated through her journal entries, capturing her thoughts and experiences as she navigates family dynamics, poverty, and her budding romance. Cassandra lives with her eccentric family, including her sister Rose, her father James Mortmain, and their stepmother Topaz. The arrival of two wealthy brothers, Simon and Neil, changes their lives, leading to unexpected relationships and self-discovery. The novel explores themes of love, aspiration, and the challenges of growing up.