Move forward and insert Cortana into the marked console.
After the cutscene, move into the portal in front of you to be transported to who knows where.
Move forward and head up into this ominous purple light.
Some...things take off as soon as you enter. Huh. Keep going forward.
...aaaaaand they're back. These things are Crawlers but they're pretty easy to down. A simple headshot will do the trick.
When they're gone, head forward to activate the light bridge.
Continue along the path and...
In this room, you'll see a bunch more enemies teleport away. Keep moving forward. Get ready...
Aaaand they're back again. Crawlers and Knights will attack you. Knights are basically the Promethean verison of Elites in this game.
When they're all dead, follow the objective marker.
Hey what's up, haven't seen you in a while! Take down all the Crawlers and Knights that spawn here.
There will also be a new enemy here, a Watcher. These annoying things fly around shooting you and healing Prometheans, so make them your highest priority.
Keep heading forward as you take down Promethean forces. There aren't a whole lot and the path is pretty straightforward.
Head up this ramp and through the door that opens up.
Before you get to the other side, take a left when the path branches for an ammo cache! My weapon choices here for the majority of the level were the Lightrifle and Scattershot.
In this room, you'll have to destroy the 3 cores to bring down the first pylon, but be careful: there's a lot of Prometheans in here. Be careful and follow your objective markers.
Once all 3 are destroyed, an objective marker will appear in the large middle structure. Follow it up the ramps.
Keep following the path and activate this elevator.
When at the top, rush forward and disable the first beam array.
One down, one to go. A portal will open up after you shut it down. Head into it to be transported back to where you started the mission.
Well that's awesome, because the Prometheans weren't already enough to deal with. Head through the new portal that's opened up in front of you and follow the corridors.
Looks like you caught a break: the Covenant and Prometheans are too busy fighting each other to focus on Chief right now. Take them all down, or let them kill each other!
Fight your way to this ramp and head up it. Plenty more enemies on it so be careful.
Hey, some unguarded Ghosts! The Covenant just love leaving all their vehicles unguarded, huh? Grab one and move forward past the enemy forces down below.
Hug the wall while moving forward and go through this tunnel with glowing cracks in the ground.
Eventually you'll come to a large room where you again have to destroy the 3 cores. If you want, you can run down this Elite and jack his Banshee before he gets into it and use it to destroy the Banshees shooting at you.
Once they're down, same drill as before: run up the ramps in the large middle structure and get to the top, watching out for the Elites up there.
Activate the elevator and head up, and disable the second beam array.
A new portal will open and again take you back to where you began the mission. Run through the new portal that's open there.
Kill the Grunts and the Jackal sniper up ahead, then activate either one of the doors to your side and head up.
Prometheans and Covenant will be fighting each other again. Take advantage of the opportunity and kill them all. A door ahead of you will open up when they're all dead.
Step onto this elevator to be raised up and head through the door to emerge into yet another battle.
After fighting your way through them, you will come up to a platform with the console you need, but is being guarded by Promethean Knights and an eyeball thingy that shoots lasers at you. If you want, just book it past them and get to the console!
At this point, all you have to do is book it using one of the Ghosts in front of you! Use your unlimited boost to make it out before you're crushed!