Years have passed since the chief was stranded in space, he is awoken by cortona and he is sucked into a for-runner structure which houses other stranded ships (of all factions) and for-runner tech. Although there are friendly factions inside the structure they have become insane, they have adapted their weapons with for-runner tech which explains how unsc weapons are there but they have changed (as said in halo 4 panel)
Inside the structure the war rages on and the flood is distrupting the for-runner tech which is causing security systems to engage and the for-runners to attack all factions in the structure… The chief and cortona are alone and as the story progresses a stronger bond grows between them, the chief and cortona are looking for a working ship or communications device to escape this stranded world. They find the communications device which has been tampered with by the flood, unfortunately cortona (who was placed in the system) was infected by a major computer virus (used to protect the information inside the hardrive) Cortona is screwed up, the chief is desperate to find a working ship so he can return to earth in order to save cortona…
He leaves with a bang, detonating the slip-space drive inside the almost destroyed frigate, he escapes in a for-runner ship which barely holds when escaping through the way he got in (cool cinematic) he arrives at earth only to find the elites have turned against the humans… earth is in tatters and cortona is messed up - it finishes with a cliff hanger… The elites need to be destroyed and cortona needs to be saved before she goes beserk
6 - kill cortona?