Chief crash lands on the forerunner shield world, only to find that the Covenant have broken their truce and have tracked his ship. For the first few levels you fight your way through the covenant until reinforcements arrive. You then begin learning more and more about the Forerunners who once resided there, and fight among their ruined buildings. Upon reinforcements arriving, a strange force pulls the Forward until Dawn into a crash landing. You then awaken the Forerunner Machines which guard the tomb or "Cryptum" of the Didact, in which he will arise.