When you start this quest you will arrive in a large room, if you go forward and then turn right instead of continuing on, you will come across a welkynd stone that is a lever. Pull this lever and the wall to the left of it will open, this is the first secret area of this quest with a hidden ghost boss behind it alongside a silver chest. Once you are done with this secret area, go back to the main room, and continue onwards. Eventually, you will reach another large room with two ghosts in it.
As you walk through the next hallway a ghost will attack you, dispatch it and continue. Further along, you will encounter a necromancer and then enter another large room, in this room there is another ghost and another welkynd stone lever to the second and final secret room. In this secret room there is a necromancer boss and a silver chest.
Once you are finished with the secret room, head back into the main room and up the staircase into another large room with chairs and a large welkynd stone in the middle. In this room there is a necromancer and a ghost, defeat them and continue onto the next room. In the next room there are yet another two necromancers, after they have been killed, head into the next and final room where the lich boss will be waiting for you.