Twelve year-old Derby Shrewd lives in a divided town. Lights live on the Northside of the Line, Darks live on the Southside. Hillside has been that way ever since the Line appeared naturally from the ground, much like a spring welling up from deep inside the earth. Now the Line controls the town, keeping Hillside separated, zapping those who come near it and killing those who dare cross it. But when Derby, a Northsider, finds a pile of bones stacked on the Line, he sets out to uncover the person's identity. While doing so, he befriends a Southside girl and soon begins to challenge the Line and the town's rules. And then, before he can turn back, Derby goes too far.