The Ritual (Quest) - Star Wars: The Old Republic
The Ritual (Quest - Sith Inquisitor class)
Having promised to help the Gormak shaman Hadrik leave Voss in exchange for his help, you head to the Dark Heart ritual site in the Nightmare Lands to perform the ritual that will heal your fractured mind and silence the ghosts.
This mission involves fighting your way through a non-instanced dungeon to reach the instanced space. Be warned that a death in the instanced area means running all the way back from a med center (you can't revive with a probe droid inside the instance) and likely fighting your way through all the respawns in the non-instanced area.
When fighting the end boss, Horak-Mul, watch for induction attacks that can be interrupted. He will heal himself with Regeneration, and do heavy damage with Force Storm - these two inductions in particular need to be interrupted whenever possible.