Seems a few people still haven't found the starter NPC for this quest so here's the info you need.
Go to Old Tarantia stables and speak to the Gutter Rat (803, 475) to get the quest to find Kalanthes in Khemi.
In Khemi you will find your old mentor near the Khitan traveller (1160, 862) who will then send you to Dragon Spine to find the entrance to the instance.
Once in Dragon Spine, head to the Shadowy Cave res pad (1100, 798) then travel southwest through a short canyon to a large defile containing the T5 vendors, the currently inactive entrance to the Palace of Cetriss and, on the north side, the portal to the Otherworldly Crossroads. Use this to enter the instance lobby and speak to Chike the Augur to advance the quest to the first boss encounter, Yakhmar.
That's all I know so far, if any are willing to share further information please add to this post or I will attempt to update it as and when I learn the strategies for each boss.