The Magicians

Lev Grossman's The Magicians is essentially "what if the Harry Potter world was populated with actual teenagers who are messed up and obsessed with sex like real teenagers are. Also Narnia". It works surprisingly well, with Grossman throwing in references to many other stories and ideas without going over the top or seeming inauthentic or corny. It's very much set in our modern world, except when the characters sometimes step out into more magical worlds that are related to our world in various ways. It's an excellent read.