Nell Crane has always been an outsider. In a city devastated by an epidemic, where survivors are all missing parts-an arm, a leg, an eye-her father is the famed scientist who created the biomechanical limbs everyone now uses.

But Nell is the only one whose mechanical piece is on the inside: her heart. Since the childhood operation, she has ticked. Like a clock, like a bomb. As her community rebuilds, everyone is expected to contribute to the society's good...but how can Nell live up to her father's revolutionary idea when she has none of her own?

Then she finds a mannequin hand while salvaging on the beach-the first boy's hand she's ever held-and inspiration strikes. Can Nell build her own companion in a world that fears advanced technology? The deeper she sinks into this plan, the more she learns about her city-and her father, who is hiding secret experiments of his own.