In picking up from where we left off with Master Chief thrown into the calm meadow once again, he apparently slept through quite a bit of the fight, as he wakes up in a war scene with everything around him practically destroyed, including Kai, who's lying on the ground looking practically dead.
"Chief, I'm okay," is what she's able to barely mutter before he wanders off into the next room to figure out what's going on. There, he encounters Vannak and Riz holding guns to Kai's head (um, how are you seemingly alive and well and how did you get here?).
Chief tells Vannak that they were all kidnapped as kids and had their memories wiped by Dr. Halsey, but he's not believing anything out of Chief's mouth. With the guns turned on him now, Kai chimes in and attempts to get the others to believe him, but it isn't until Captain Keyes walks into the room and backs Chief up that Vannak and Riz come to their senses.
With Makee apparently on the loose with the keystones in tow, Chief convinces everyone to work together towards the main goal: to stop Makee from leaving the premises. On top of that, they attempt to stop Dr. Halsey, as well, who's also fleeing the UNSC base on a stolen ship. Though Kai was able to remarkably make it onto that ship, Halsey was able to jump ship in an escape pod at the last second. Later on, the UNSC locate Halsey and take her into custody. Oh, and Makee was able to get away, which means that the Spartans will have to figure out where the Covenant's base is and locate the keystones.
Halsey is only in custody briefly, dying quickly after losing control of her body. However, Dr. Keyes remembers that when her mother would flash clone the baby-Spartans, they would also die in a similar manner, which means that Halsey flash cloned herself and was not actually the woman in custody.
With Makee on the run, Chief takes the reins of a UNSC ship and—with Cortana's help—attempts to figure out just where Makee and the keystones are. Knowing only small tidbits of information about their possible locale, Cortana pieces them together and finds a destination. The only problem? They might not even be able to make it to that part of the galaxy as gravity has started to pull them in different directions. Ah, the beauty of space.
I didn't play the Halo video game campaigns, but damn Master Chief, who knew you were such a good pilot? You go Glen Coco! I mean, he just flew through a random part of space while basically being split in half by gravity and all he got was nothing. Well, he didn't die, so I guess that counts as something.
Anyway, instead of landing the aircraft, the Spartans decide to jump out of the ship and land on the planet that way. But when they land on the ground, they land in half-kneeling positions—how is that physically possible? No broken knees? Or death? Okay.
Upon landing, they encounter hundreds of Covenant troops almost immediately, and given that there are only four Spartans, things don't look great. The Spartans are able to hold the Covenant off for some time, but they're taking an absolute beating from the aliens.