Brothers Cal and Niko Leandros know trouble when they see it—and then proceed to wipe the floor with it. But now it seems their whole world is falling to pieces. Cal’s nightmarish monster side is growing ever stronger, changing Cal physically as well as mentally. Which is exactly what Grimm—Cal’s savage doppelgänger—wants. And when a covert supernatural organization decides that it’s time to put Cal down before he threatens pretty much everything else in existence, the brothers find themselves in a fight they actually might lose. But the dark temptations Cal has denied all his life may prove to be exactly what can save them.