A Famine of Crows — A.A. Chamberlynn

The Riders may have kept the sixth seal from being broken, but the Apocalypse is far from over. Four new Riders have emerged with the sole purpose of hunting and destroying them. Atsa is still imprisoned in the realm of Spider Woman. And their powers, including the elemental magic they discovered, are far from within their control.In order to survive, the Riders must split up. Felicity and Dynah work on deciphering the spell in Sekhmet's book while Willow and Penelope go in search of a half-angel who might be the only one who can tutor them. That is, if she doesn't kill them first. Time is running out, and it's more than their lives at stake: the whole world hangs in the balance.