Hitting The Books takes you to Fellglow Keep. This problem seems to be new in the Steam PC version of the game. The path to the stairs that leads to the door to the Caller, and the books, is blocked. I used Creation Kit to remove the stones and went up the stairs to find the door was missing. Now that door is in Skyrim so one of my mods is deleting it. I used Creation Kit to put in the correct door and the rest worked fine until I tried to use the quick exit from the Caller. Going through that door put me into empty space far above where I was supposed to be. Hovever, falling through the architecture I landed ok and was able to finish the quest. The first glitch is in vanilla Skyrim. The rest are in an unknown mod.