Reclaim Krasus's Compendium - Chapter 1, Krasus's Compendium - Chapter 2, and Krasus's Compendium - Chapter 3 from Kirin'Var Village's Town Square. Use Archmage Vargoth's Staff to contact the archmage once you have the chapters. If you lose Archmage Vargoth's Staff, speak to Ravandwyr at Area 52 to receive a replacement.
The Kirin Tor sent one other of Krasus's possessions with our expedition. It was his spellbook, called Krasus's Compendium. Containing all the spells he mastered, it lent us a much-needed advantage in the war.
Before Kael'thas and his forces laid siege to Kirin'Var, the compendium had been stolen from me by a rebellious apprentice intent on studying necromancy. The apprentice and his followers divided and studied the text in secret, locking themselves inside their houses in the southern part of town.