Now, watch me.
Sut put the Freezing Eye and Blood into an old water bottle. The items melded together and formed a scarlet crystal.
Use this Dark Frozen Crystal at the ruin in the east of the Vilefiend Spire, and the plotter will be forced to show up.
If you can get rid of him (or her, I'm an equal opportunity mage), you'll quell the demon spirits' insane uprising.