halo ce
halo combat evolved starts when the pillar of autumn comes out of slip space and finds halo and then is boarded by the covenant and crash lands on alpha halo the master chief 
rounded up the survivors and boarded a covenant ship and recued captain keys and keys went to find a weapons cash which turned out to be a trap the covenant had found a forerunner containment facility that held the flood a parasite. the flood killed and infected everything in its path keys was with the team that went to the cash he was lost. master chief and Cortana went back to the ship they bored earlier that was now flood infested they found keys he was part of a proto gravemind chief killed keys and the proto gravemind chief took command codes chief took the codes to the autumn and detonated the autumns reactor and destroyed alpha halo he and Cortana escaped.