The Rithmatist, by Brandon Sanderson, is what I like to think of as classic "fun" Sanderson. By that I mean that it's a fast-paced, mystery-adventure set in a fantasy world with one of Sanderson's trademark amazing and complex magic systems (Rithmatics -- chalk drawings are imbued with two-dimensional power in the hands of a Rithmatist. It's geometry come to life).
Joel is the son of a chalkmaker, an ordinary, non-Rithmatist. Joel is a smart kid who regularly fails classes just because he doesn't find them interesting. He's obsessed with Rithmatics, and can draw Rithamtic defenses and offenses as well as or better than many of the Rithmatic students he attends school with. He knows a lot of people, but doesn't really have any friends.
Melody is the fourth Rithmatist child of Rithamtist parents. She's bold and outspoken, a bit of a dramatic free spirit. She's not that good at Rithmatic lines and circles, and feels the pressure pretty intensely (although she's very gifted at drawing the chalk creatures called chalklings). She's not very popular, and sometimes coves up that loneliness with loudness. Oh, and her favorite chalklings are unicorns.
Melody and Joel end up spending their summer elective being tutored by the same professor -- a brilliant, kindly, but recently professionally humiliated Professor Fitch. The summer brings with it a rash of mysterious disappearances of Rithmatic students, and a lot of resulting rumors and unrest in the American Isles. Melody, Joel, and Fitch end up personally involved in the mystery and the dramatic conclusion that brings up a lot of questions and reveals a very mysterious and dark potential villian. In the meantime, the two loners begin to grow the kind of frienship in which each person is pushed to be better (there's a scene at the end of the book that KICKS BUTT. These two are going to be a powerful duo).
Bottom line: if you like mysteries, adventures, cool magic systems, fantasy, friendships or all of the above -- read this book.