Thirteen years ago, a radical fertility doctor helped bring Adam and Alice Twisden into the world. The treatment came at a great cost: it turned the twins' parents into barbarous animals and threatens to transform the children, too. As Adam and Alice find themselves on the brink of maturity, they starve themselves in a desperate attempt to stop their bodies from changing. Will they succumb to the same bodily horrors that destroyed their parents?

Their aunt, Cynthia, who has always wanted to be a mother, oversees renovations to the Twisden family's Upper East Side residence-violently torn apart by the children's parents -- and struggles to give her niece and nephew the unconditional love and stable home life they never had. Meanwhile, in the world outside, the forces of good and evil collide as a troop of wild teenagers, growing steadily in number, threatens to invade the calm refuge Cynthia is so determined to construct behind the safety of the Twisdens' walls.

As New York City transforms into a battleground, Adam and Alice will have to decide where their loyalties lie. They are determined to lead normal lives -- and yet their unnatural urges, which grow ever stronger by the day, can only be stifled for so long...