Long Drop Full Stop

Shoot a rope arrow at the beam near the window, Climb the nearby crates and circle around on the roof tops. Cross the street using the long beam, and turn left at the platform, Around the corner is your rope. Tarzan your way to the window, and climb inside.

Examine the books in the back of the room for a hidden switch. This opens a new area, which has the book you're after, as well as some other goodies.