Defeat Teraks's platoon near the Crux of Darkness in Eternity.
"Let's cap it off with a bit of Ether. Another of House Salvation's 'elite' have taken residence over in the Exoscience building. Put an end to it." —The Exo Stranger
The Skeleton Key is almost ready. The Stranger believes one more boost of energy from combatants near a Crux should do it. Find Teraks, Salvation Elite Captain and eliminate their platoon.