Morrigan's Cross book by Nora Roberts

The Circle Trilogy begins with an epic tale that breaks down the boundaries between reality and the otherworldly, while forging together the passions of the men and women caught in a battle for the fate of humanity… In the last days of high summer, with lightning striking blue in a black sky, the sorcerer stood on a high cliff overlooking the raging sea… Belting out his grief into the storm, Hoyt Mac Cionaoith rails against the evil that has torn his twin brother from their family’s embrace. Her name is Lilith. Existing for over a thousand years, she has lured countless men to an immortal doom with her soul-stealing kiss. But now, this woman known as vampire will stop at nothing until she rules this world—and those beyond it… Hoyt is no match for the dark siren. But his powers come from the goddess Morrigan, and it is through her that he will get his chance at vengeance. At Morrigan’s charge, he must gather five others to form a ring of power strong enough to overcome Lilith. A circle of six: himself, the witch, the warrior, the scholar, the one of many forms, and the one he’s lost. And it is in this circle, hundreds of years in the future, where Hoyt will learn how strong his spirit—and his heart—have become… Don’t miss the other books in the Circle Trilogy Dance of the Gods Valley of Silence Published By Penguin on 2006-08-29