It is 2555, more than two years after the Master Chiefwent missing-in-action following a decisive conflict on themassive, extragalactic Forerunner construct known as theArk as part of the final chapter in humanity's bloody thirty-yearstruggle against the overwhelming forces of theCovenant. When a startling scientific discovery is made,ahastily formed coalition of humans and Elites embark on acovert mission back to the Ark to save the entire galaxy.