Find the Book of Necromancer

There are two routes to the Book:

1. From the cathedral area
From the front door of the cathedral, turn right (West) and walk through the cemetery.  The single wooden door to the left of the banner ahead is the library entrance.  Pick the lock, go in and up the steps.  Operate the lever on the wall of the guardpost to open the metal door.  Go through and up again.  Turn right at the junction  and up a couple of steps to the passage with the wooden floor (by the banner).  Go up the wooden steps and turn right into the lower library.  Operate the lever between the bookcases on the right, walk forward a few paces and slash the banner on the East wall  to reveal the Book of Necromancer.

or

2. From the main hall
From the main hall, go down the steps to the North and pick open the wooden door ahead.  Follow the passage clockwise until you come to the double doors in the North wall.   Go through, and turn East into the barracks room and then West out of the other door.  You are now in the top level of the library.  Go down the stone steps on the right to the lower level.  The Book is behind the banner on the East wall.   Walk East then North - the lever to open the panel is between the two bookcases on your left.  Slash the banner and grab the Book.