Zia, a young Native American girl, struggles to reconcile her heritage with the encroaching influence of the Spanish mission system while attempting to rescue her aunt, Karana, from the Island of the Blue Dolphins. Zia lives in a world defined by the rigid hierarchy of the California missions and the harsh realities of colonial expansion. Her primary objective is to secure the freedom of her aunt, who has been stranded alone on a remote island for years. She faces opposition from mission authorities and the physical limitations of the rugged coastal environment. The narrative follows her perspective as she navigates the cultural divide between her indigenous roots and the life forced upon her by the mission fathers.

Readers frequently highlight the stark, minimalist prose style that mirrors the harsh environment of the protagonist. Discussion often centers on the thematic weight of cultural assimilation and the loss of traditional ways of life. Critics note the effectiveness of the book in portraying the quiet resilience required to survive in a changing world. The balance between character-driven introspection and the external pressures of the mission setting remains a frequent point of analysis for those examining the work's historical accuracy and emotional resonance.