This, the second book in 'The Magicians' series tells of Quentin and his friends in the imaginal world of Fillory. Some of the characters have come about their magical skills and knowledge via the channels of academia (as told in the first book), while others have come about theirs in a more illicit manner -- learning from the magic 'underworld', if you will. Together, they work to find the source of magic that is Fillory, without which it would cease to exist, and that very source is under attack. As with the first book, 'The Magicians', the tone of this story is dark, the energy primordial and raw. There are things that can go dreadfully wrong and they do.
*Caution: Swearing and strong language throughout (unnecessary, in my opinion).