This quest is not available in game.
Using the Pure Hearts, summon and subdue a succubus, then return the Pure Hearts to Carendin Halgar in the Magic Quarter of the Undercity.
Using these hearts, cast a spell at the summoning circle to open a doorway for the succubus to come through. Your powers are greater now, and you will need all of them to defeat the succubus.
Beware its charms, <name>, many a strong mind has been bound to its will. When overcome, the succubus will be returned to the void, and I will teach you the spell to summon it forth at your command.