Grim(oire) Business

There is one more gronn to be slain: Skulloc Soulgrinder. He keeps himself hidden away, but there is a way to coax him forth.$B$BHe was trained by an ogre warlock known as Vim'gol the Vile, whose grimoire you must retrieve!$B$BVim'gol must be summoned by standing within a fire ring at his circle. Find Vim'gol's Circle in the mountains, to the northeast, near the Broken Wilds.$B$B$N, if you hear Vim'gol talk about growing bigger, get people back into each of the five fire rings to interrupt his casting!