For step 3 below, the disruptive students spawn throughout the library (upstairs and downstairs). Since it is a timed event, you are advised to clear all the trash in the library before carrying out step 2 (which starts the timed event).
Shadowed Corridors: The Sealed Ancient Scroll can be obtained on the first floor. On entering the south-east room, a shadowbeast spawns. Kill that, and a Large Undead Gnoll spawns. Defeat that, and a small chest drops containing the scroll. You may need to clear the rooms multiple times to get the large one to spawn.
Return to Marian Cross at ( -75, 49, 78 ) /waypoint -75, 49, 78 in the frozen library. She deciphers the book for you and gives you excerpts of each chapter. She tells you that the book's author is Cara Omica and you need to speak to her.