This is an access quest. Completing it gives access to the back door to the Ruins of Varsoon. It is given by Zaen Kalystir at +51, 0, -163 in the Vermin's Snye.
The first step is to visit the Tomb of Varsoon in Antonica. This is on the Forbidden Island at +360, -20, -663 (northwest portion of the zone). After doing this return to Zaen Kalystir.
The second step involves traveling to the hidden entrance to the Ruins of Varsoon in the Thundering Steppes. This is the cave guarded by goblins and skeletons near the skeletal veterans along the wall, not far from the normal entrance to Varsoon (-483, +3.88, +1064).
This will open up the Into the Crypt of Betrayal quest.