Return the book to its rightful owners.
It can be difficult to find the library, which can actually be accessed from either Dire Maul North or Dire Maul West. The simplest way is through Dire Maul North. After you enter the instance, go down the first ramp into the pit (full of ogres and dogs). To the left in the pit is a locked door which requires [Crescent Key] or 300 lockpicking. Through this door is a long hallway which leads into the Aethenaeum library (actually part of Dire Maul West). As you enter the library, Kildrath will be to the left (south), muttering about other lost books.
Patch 1.3.0 (07-Mar-2005): Added.