Set primarily on the "rogue" Halo ring Installation 07 used by Mendicant Bias during the events of Cryptum, the novel follows the journey of the humans Chakas and Morning Riser, former companions of Bornstellar Makes Eternal Lasting. After crash-landing on the Halo ring during Mendicant Bias' assault on the capital, they discover it has been used by the Master Builder's researchers to conduct research on humans. They are forced to make their way across the embattled Halo installation, facing the Flood and rogue A.I. constructs on the way, while the Precursors' ancient plan of vengeance against the Forerunners is revealed. During their journey, they find their way into the Palace of Pain, the lair of the ancient entity known as the Timeless One, which has unleashed The Flood on the Master Builder's researchers on the installation. Mendicant Bias will also play a major role in the story.
Frank O'Connor has mentioned that the story is "closer to the ground" than that of Cryptum, and that it will have "resonant connections" to Halo 4. Greg Bear has hinted at a connection between John-117 and one of the novel's human characters. He also confirmed that the novel will explore the Precursors' plan, and that it may cover events that occurred up to three billion years before the events of Halo: Combat Evolved.