Captain Jacob Keyes of the Pillar of Autumn has been taken hostage by the Covenant. With the help of your Marines, infiltrate the Covenant ship called the Truth and Reconciliation and rescue him.
You will be dropped off by a Pelican along with a small team of Marines. You will have the Assault Rifle and the Sniper Rifle with you and it is night time. From the start, turn left and follow the small path on the right-hand size. Try to stay as inconspicuous as possible for the beginning of this level, but remember the enemy becomes active once you make the surprise shot. Use your Sniper Rifle's 10x scope and start shooting at the Grunts stationed in the Turrets. This should cause a small ruckus in the Covenant camp and they should start running around, giving you a clear shot at them. First take out the Elites. If you are spotted, the Covenant will shoot at you and your scope will be rendered useless, but your allied marines will also attack. Make good use of this time that you are invisible to them. Once you clear this place of Covenant, switch your Assault Rifle for a Plasma Rifle (if you can find one, if not, just grab a Plasma Pistol).
As you are making your way to the next area, some Covenant should appear and block your path. This shouldn't be too hard as you have your Marines with you. Believe it or not, the Marines are invaluable in this game. So, once you have cleared all these new Covenant, keep pushing forward and you will appear on a narrow path. Be careful not to fall off, as it will result in death.
As you make your way up the Plateau, you will see a large rock. Beyond this rock there are massive troops of Covenant. Take to the left (be extremely careful here not to fall off) and snipe out any Covenant you see. After you have taken out any possible Covenant, head forward. An Elite should attack you from the right, so have a Plasma Grenade ready. Kill all the Covenant here, and replace/restore any weapons you need and pick up the Med-Kit if you need it.
Further along, you will come upon a small opening with even more Covenant. Take them all out, and be wary of the alcove to the right holding some Grunts. Not that they will pose too much of a threat to the Master Chief. You're about half-way to the Cruiser now, don't give up!
Go forward a little bit, careful not to let any Covenant spot you. Cortana will radio in and tell the Marines to take the middle, as you take the left. On the small ledge above you, there should be an unwary Elite. Snipe him out and go forward all the way and turn to the right. Here, stick to the left wall here, sniping out any Covenant you see. If any get too close, switch out to your Plasma weapon and take them out. There is also an Active Camoflauge hidden by some trees. There are some Elites guarding it, however, so you might want to take them out first. The AC (Active Camoflauge) is useless if you are somehow shot, so don't get in the crossfire of the Marines and the Covenant. After you take out all the Covenant to the left, start sniping out any Grunts manning the Shades (those are the Covenant turrets). Congrats if you made it thus far, this area is pretty hard, even on Normal.
Now join your Marines in the middle fighting off the Covenant. There are Grunts, Jackals, and Elites, so be careful. Once you finish this, continue along the path. Cortana will radio in and order for some more Marines. A Pelican will arrive and the Marines will jump out the back. Continue forward. Be warned, though, a massive fight lies ahead...
As you make your way along the path you will see a large opening surrounded by Shades. Pick out the Grunts in the Shades, then the Elites. Continue pressing forward, killing any Covenant you see. If you rush through fast enough, you will leave the Marines way behind, and, thinking their dead, Cortana will radio in for some more Marines. This is pretty good, though not exactly the best move on the harder difficulties. But, then on the Easier difficulties, you really won't need the additional Marines. Sucks how it's like it...
You have probably noticed a large purple beam shooting from the Platform and into the Covenant Cruiser. This is a Gravity Lift which will transport you and your Marines into the Cruiser. Before you can make it, however, more Covenant will descend from it. Kill off any that come. After several waves have appeared and destroyed by your supreme skills, the music will change dramatically, signaling an approach of a new challenging enemy. Two hunters will descend from the lift, which are large shield-wielding Covenant that travel in pairs. As they descend, take out your Sniper and head off to the back edges of the opening. Start shooting at the back of the Hunters at their orange spots. A couple shots should be able to kill one. If you're not fast enough, however, your Marines will be slaughtered almost instantly. As you have prevailed over these cursed beasts, you will be able to ascend into the ship. Step onto the Gravity Lift to continue to the next area.
Into the Belly of the Beast[edit]
You have boarded the Covenant Cruiser where Keyes is supposed to be found. Find the brig and rescue Keyes.
You thought it would be the next level, didn't you? Nope, this is only the second half!
You will appear in a large room with some boxes and unoccupied Covenant Tanks called Wraiths. The lack of enemies is a trap. The doors will open and some Grunts, Jackals, and Elites will appear, starting with invisible Elites wielding swords. Getting hit by a plasma sword will result in a one hit kill, so take them out quickly as they will slaughter your Marines even faster than the Hunters. They don't take as many hits as the regular Elites do, and also become visible if you can hit them. If you want, you can pick up the AC behind some boxes and enter the doors where the Covenant appear. Pick out any Covenant you see along these halls before they can get to your Marines. Once you have killed every Covenant soldier in this area, your Marines will advance through a large corridor. You will see a door not too far down, but, unfortunately, it is locked. Make your way back up the corridor and head through one of the doors the Covenant came from. Keep going down these narrow halls, killing any Covenant you see, until you come to a walkway overlooking a large room with Covenant. Take out any Covenant on the walkway before getting to the ones below you. Use your Sniper Rifle (if you still have bullets) to take out some of the Covenant below. Once you have killed off enough Covenant, jump down (be careful where you land, as too big of a fall can be dangerous) and open the door. Your Marines will come through and help you kill off any Covenant.
Once you have killed off all the Covenant and have your Marines by your side, some more Covenant troops will advance through a door and attack you. Take them out and go through the door they appeared from. Keep going while killing off the Covenant forces until you arrive at the Shuttle Bay. In this area, there will a large platform above you with some Elites and Jackals. Take them out with your Sniper, assuming you still have ammo. If not... well, good luck! Pick up the Med-Kit here if you need it, as well as the Over Shield, which grants you two more life bars. After killing all the Covenant here (this will probably take some time, however), then two Hunters will appear behind some doors. The music will change again and you will have to kill them before they defeat your Marines. Once you kill the Hunters, then follow the Navigation Point to the doors and advance. Continue along the way, kill the Covenant, etc. Eventually, you will be at the second-most upper platforms of the Shuttle Bay. Here you can push the switch to open the Shuttle Bay doors, allowing a Pelican to come in and drop off some Marines. As soon as the Marines appear, some Covenant will appear from the doors you just came from. Crafty little buggers! Take them out as you normally would and keep going forward to come to the very highest levels of the Shuttle Bay.
Follow the ledge to the right while killing the Covenant. Use frag grenades to your advantage while you continue advancing. Go through the doors at the end of the hall and continue through these passages until you reach a three-way fork. The left path leads you to some health and ammo, while the center and left paths take you to the Control Room.
The good news is, you have you Marines. The bad news is, this area is tough. The other bad news is, your Marines don't really help you. When you open the door, you will find some snoozing Grunts and some marching Elites with swords. Melee the sleeping Grunts to instant KO them, then retreat as soon as the sword-wielding Elites start advancing towards you. If you have good aim, throw a Plasma Grenade at him as you continue moving backwards. If he catches up with you with the Grenade stuck to him, you will killed or seriously wounded by the explosion, so be careful.
Once this room has been cleared, your Marines will stay behind and "guard" this area. Keep moving forward until you reach the Holding Cells. Kill the Covenant here, which include two invisible Elites. After that, open the cell doors, releasing the captive Marines, including Keyes.
Shut Up and Get Behind Me... Sir[edit]
You have rescued Captain Jacob Keyes, as well as some additional Marines. Now, escape the Cruiser with Keyes alive.
This chapter is pretty small, and is also the last one for this level. Also, you must keep Keyes alive, as you will lose if he dies. Head back to the Control Room to find your Marines... dead. Two invisible Elites with swords are patrolling this area. Take them out quickly, before they can get to Keyes. After that, you will find out that the EVAC that was supposed to pick you up is currently in battle with some Covenant forces. "Aw man, we're screwed!" Not really. Kill the Covenant that come into this room, protecting Keyes, until the waves of troops finally stop. A Navigation Point will appear, leading you back to the Shuttle Bay. Kill the Covenant here and press the button where the Navigation Point is. After a while, a movie will trigger and you escape in a Covenant Dropship. You win. Onto the next level!