The Trail of Bones - Chapter 3

The news I have upon your return is no better I fear. The Druchii had carted off your Nehekharan relics far to the south long before you arrived. They are already in Saphery preparing the relics for some dark ritual of unbinding at the Stone of Avatheys. The Druchii must be stopped before they unleash the wind of Shyish upon Ulthuan. The relics are there, in Silverglass, or the ruins of Silverglass. Make haste, for Ulthuan's sake.

Travel south into Saphery towards the town of Silverglass. Confront the Druchii at the Stone of Avatheys, and complete the Sweating the Stone public quest. Afterwards travel to the ruins of Silverglass and collect any Nehekharan Relics you see, and check the surrounding area for a reliquary that could have been inside the artifact chest. Check it for the Seal Piece.