Atlee Pine, an FBI special agent, is called in to investigate the mutilated carcass of a mule found in the Grand Canyon--and hopefully, solve the disappearance of its rider. But this isn't the only recent disappearance. In fact, it may be just the first clue, the key to unraveling a rash of other similar missing persons cases in the canyon.

For many long years, Atlee Pine was tormented by uncertainty after her twin sister, Mercy, was abducted at the age of six and never seen again. Now, just as Atlee is pressured to end her investigation into Mercy's disappearance, she finally gets her most promising breakthrough yet: the identity of her sister's kidnapper, Ito Vincenzo. With time running out, Atlee and her assistant Carol Blum race to Vincenzo's last known location in Trenton, New Jersey...