The Magicians by Lev Grossman
As a senior in high school Quentin Coldwater became preoccupied with a series of fantasy novels he read as a child, set in a magical land called Fillory. After graduating from college and being admitted into a highly exclusive, secret society of magic in upstate New York, he makes a stunning discovery: Fillory is real. But the land of Quentin’s fantasies turns out to be much darker and more dangerous than he could have imagined–for his childhood dream becomes a nightmare with a shocking truth at its heart.