Marooned with Senior Chief Petty Officer Franklin Mendez and a Spartan team in a Forerunner slipspace bubble hidden in the destroyed planet Onyx, Halsey finds that this place has been guarding an ancient secret—a treasure trove of Forerunner technology that will change everything for the UNSC and mankind. As Kilo-Five joins the hunt for Halsey, humanity’s violent past begins to catch up with all of them as the disgruntled colony Venezia has been biding its time to strike at Earth…and its most dangerous terrorist has an old, painful link with both Halsey and Kilo-Five that will test everyone’s loyalty to the limit.