Nick tried to chase down the invisible enemy but was unable to stop them. He saw a (seemingly riderless) spectral steed ride off into the distance and disappear. Realizing you had lost your invisible assailant you returned to working your way through the lair.
You cleared out a room of bonedrinkers, and defeated a ghost dire lion in another room.
In another room you find a massive sphere of polished black stone. You left it alone and continued forward.
You eventually enter a room and are confronted by the Ghostlord who demands you explain who you are and what you are doing in his domain. You explain that you have his phylactery which you took from the Red Hand. He then demands you give it to him at once. You tell him you will give it to him only if he assists in the upcoming battle. When he asks why he shouldn’t just kill you and take it, you manage to convince him that you have it stored somewhere else and he will not find it if he kills you. He seems very annoyed and angry but agrees.
You quickly leave his lair before he decides to kill you anyway.