"I Capture the Castle" is a coming-of-age novel that tells the story of 17-year-old Cassandra Mortmain and her eccentric family living in a dilapidated English castle during the 1930s. Cassandra's father is a reclusive writer suffering from writer's block and her stepmother is a bohemian artist. The family's life changes dramatically when two American brothers inherit the estate. The novel, written in diary format, explores themes of love, poverty, and the transition from adolescence to adulthood.

The book follows the adventures of an inquisitive and fiercely independent eleven-year-old girl who loves to write and aspires to be a spy. Armed with her trusty notebook, she observes her friends, family, and neighbors, jotting down candid and sometimes unkind notes about them. Her world turns upside down when her secret notebook is discovered and read by her classmates, leading to a backlash that tests her friendships and her understanding of honesty and privacy. Through her trials, she learns valuable lessons about empathy, trust, and the consequences of her actions.

The book is a semi-autobiographical novel that follows a Native American teenager who leaves his school on the Spokane Indian Reservation to attend an all-white high school in a neighboring town. The protagonist grapples with his own identity, the perceptions and prejudices of his new classmates, and the harsh realities of life on the reservation. Throughout the story, he uses humor and his passion for drawing cartoons to navigate the challenges he encounters.

The book is a humorous portrayal of the protagonist's daily life as he navigates the trials and tribulations of middle school. Through his diary entries, the reader gets a glimpse into his struggles with family, friends, and school. With a unique blend of text and cartoons, the book provides an engaging and relatable depiction of the protagonist's attempts to gain popularity and survive the school year, despite his many embarrassing incidents and frequent misadventures.