Definaltly a must for a raiding Paladin. Pick up the book from the AH or from DM as a drop if your lucky. Can be solo'd by heading into DM north. Wait for Ogre to walk away from ramp down into the courtyard then head down and jump up onto the left ledge of the ramp. Hug the left wall and go down second ramp to locked door. Must have the DM key obtained from DM east or a truesilver skeleton key should do the trick, (only tried this on outside door). Once thru door just head down the unoccupied cooridor to the Library and turn in to Lorekeeper Mykos, and you will be rewarded with a trinket providing +10 Fire resist and Equip bonus' of +150 armor and +22 healing!

One thing to note is that for a lvl 60 picking up the quest from Feathermoon Hold to locate the missing NPC is a good quest to get before heading into DM. The body you need to use to complete quest is in library and rewards 6+ gold. Sorry but I can't remember the exact quest name but it is given from the NPC that wanders behind the inn at Feathermoon.

14300xp at level 54 as of this post (patch 2.3.3)

who do you give it too?

?user=LorekeeperMykos"">LorekeeperMykos said: <div class=""pad"">As time passes, we tend to change around and even add new rewards for the return of missing tomes.He must be talking about ""changing around"" on a timescale of millennias.
Doesn't seem like he will ever offer anything else in reward, does it?