Certain Magical Index, Vol. 7 (light novel) by Kazuma Kamachi, Kiyotaka Haimura

A legendary tome known as The Book of the Law, which describes how to summon an angel, has been stolenand the nun who knows how to decipher it has been kidnapped. All of which should be completely irrelevant to high school student Touma Kamijou, who's still whiling away his time in Academy City. Except his famously terrible luck gets him involved in the rescue operation, and if he thought school life was bad enough, wait until he gets a taste of church politics!