Natividad is Pure, one of the rare girls born able to wield magic. Pure magic can protect humans against the supernatural evils they only half-acknowledge-- the blood kin or the black dogs. But before Natividad's mother can finish teaching her magic their enemies find them. Their entire village in the remote hills of Mexico is slaughtered by black dogs. Natividad and her brothers must flee across a strange country to the only possible shelter: the infamous black dogs of Dimilioc, who have sworn to protect the Pure. In the snowy forests of Vermont they must pass the tests of the Dimilioc Master.