Thanks for the answers, I'll be sure to check the top floor when I get home tonight.
>>Joram:
You'll have to take the lift to the bottom floor, there are 4 floors, and you enter the lift at the second level, so take it down one level. There you'll find a single enemy, who holds the key to the library door.
Edit: Thanks again, worked like a charm

I'm now in Trogdor-mode burninating peasents.