Uncovering the Past
This mission becomes available after Removing the Heart has been completed. Drive back to find the massive shield disabled, and minimal kett presence on the surface.
Your marker will lead you to an ice-ravine. SAM will tell you approximately one million-billion times when the temperature changes, but there are so many heatsources you're never in environmental danger.
When the ravine stars to get deep, there is a little hidden room to the left.
All it's hiding is some Iridium, but now you know.
Follow the path until you reach Kett resistance. The forces are semi randomized, but you can usually count on mostly Chosen, some Wraiths, and one Destined.
Once you start reaching the aras with actual floors, archways, and other architectural features, you'll see more Anointed thrown into the mix.
Keep going, until you pass through a large, long archway to an overlook, and are given the objective to 'Clear out kett.'
You can do that in a second, but for now hang a sharp right, heading for the question mark on your map/radar. This leads you to small storeroom.
At the very back is an Angaran Artifact you can pick up for Avela.
Now return to the overlook, and start slaughtering kett. You'll also pick up the objective to free the Angaran prisoners, which you can do as you go.
When all the prisoners & kett are free & dead, respectively, talk to the last prisoner to learn more about the site.
Scan the door he spoke of. You don't need to manually activate the charges yourself, just wait for the dialogue to run, then fall back to the objective marker and wait for the door to open. The blast is singularly unimpressive, but the room beyond is pretty neat.
Now is a good time to save your game. You're about to make an important choice, and a save here will save you trip through the entire complex again if you change your mind. When ready, walk forward to trigger a cutscene/dialogue. You wind up with a choice between killing the AI and letting the AI kill the prisoner. The paragon choice is clearly the former- you've only known this AI for a few minutes and it's already lied to you repeatedly and is about to commit murder (the first of many, for all you know). Plus, it's actively begging for death.
Unfortunately, this is also the least interesting choice, gamewise. If you spare the AI, then let it be with SAM (hey, murder totally pays off, kids!) you get some unique dialogue throughout the game. If you spare it and give it to the Angara, you get a small bonus in the final fight. No matter what choice you make, the quest itself ends here, with a burst of XP and Viability Points.