Oh I didn't see that you wrote briefly

To elaborate, the chief was put to "sleep" by cortana. I think 5 years pass or something and cortana wakes him up because there is an attack on the ship. It's an army of covenant who separated from arbiter and still worship the the forerunners. The ship the chief was on apparently floated all the way to a forerunner planet called requiem. So the chief is in there kicking ass trying to find a way home because cortana is going crazy and dying because AI's only have a 7 year life. All of a sudden they start hearing messages from a unsc ship and they try to tell it to stay away from the planet, because it sucks in everything that gets near. Chief thinks he found a communication device and destroy something's to try and communicate better but he ends up freeing an evil forerunner. The chief eventually ends up meeting with the people from the ship, who got sucked in cause they couldn't communicate in time. So they try to find a way out, eventually they do and so does the evil forerunner. He decided to go kill wart and chief chases after him. He catches up but cortana got stuck inside the forerunners ship computer system. As the chief goes 1v1 with the forerunner (not before the forerunner managed to blast a whole city) he keeps getting beat down by the forerunner. Then cortana manages to hold manifest herself and hold down the forerunner while the chief sets up a nuke. The nuke goes off and destroys the forerunner and his ship, and cortana made a shield around chief but she died in the process of the ship being destroyed. They eventually find the chief floating in mid air and he goes to a ship where they take off his armor and he sees that they've been working on a bunch of new Spartans called Spartan IV's

I see