Morrigan's Curse - Dianne K. Salerni

In the third book of the series that VOYA recommends ?for fans of Percy Jackson and Harry Potter,? the war over the Eighth Day continues?and there's more at stake than ever before. The battle between Kin and Transitioners that's been brewing for centuries has finally come to a head. The sinister Kin have captured Evangeline's younger sister, Addie, a descendant of Merlin whose presence will allow them to reverse the Eighth Day Spell and free themselves. Addie doesn't realize the full consequences..