"Obsidio" is the third book in the Illuminae Files series, written by Amie Kaufman and Jay Kristoff. It continues the story of a group of teenagers who are caught in a conflict involving a powerful corporation and an alien threat. The narrative is presented through a mix of documents, emails, and interviews, creating a unique reading experience. The plot follows Kady Grant, Ezra Mason, and their friends as they navigate the dangers of war and betrayal. As they uncover secrets and fight for survival, they must also confront their feelings for each other amidst the chaos. The book combines action, romance, and suspense in a thrilling conclusion to the series.