"Halo: The Flood" is a novel by William C. Dietz that expands on the story of the popular video game series Halo. Set during the events of the first game, it follows the crew of the UNSC Pillar of Autumn as they encounter the parasitic alien species known as the Flood. The narrative explores the struggles of the human characters against both the Flood and the Covenant, a coalition of alien races. The book provides deeper insights into the characters, including Master Chief and Cortana, while detailing the chaos unleashed by the Flood's emergence. It highlights themes of survival, sacrifice, and the consequences of war, enriching the overall lore of the Halo universe.