This quest is not available in game.
Find Ras Frostwhisper in the Scholomance. When you have found him, use the Soulbound Keepsake on his undead visage. Should you succeed in reverting him to a mortal, strike him down and recover the Human Head of Ras Frostwhisper. Take the head back to Magistrate Marduke.
There is but one task remaining, <name>. Confront the lich, Ras Frostwhisper, in his lair.
Use the power of the keepsake against the beast - be unrelenting in your actions! Weather the blows that the flailing beast will surely bring down upon you. Do not give in to the pain!
When the ritual is complete, Ras will be mortal once more. It is at that point that he must be slain. Strike him down and take his human head.