Stone Of Souls 2: Stone Parts

I found the first necromancer on the east, deep in catacombs of the old castle. He was not waiting for me, so I got Stone of Souls quite easily. But as soon as I got it, I felt that it was only one part of the artifact, I have to find another three pieces to gather these relics into one artifact and stop all the madmen who summon evil spirits from the world of the dead.