Blood magick / Nora Roberts.

In Dark Witch and Shadow Spell Nora Roberts introduced three cousins - Iona, Connor and Branna. They share a close bond and a dark gift, handed down through the generations. They use their powers for good, but are under constant attack from a powerful enemy called Cabhan. He will stop at nothing to destroy the cousins and take their powers for his own evil purposes. Their struggles have brought tragedy to the cousins' lives but it has also brought hope and love - at least for Connor and Iona, who both found their soulmates despite their battles. Branna, however, has a more troubled history. The man she truly loves, beneath it all, is Finbar Burke, but he is a descendant of Cabhan. While Fin has proved himself an ally, Branna mistrusts him. Can Fin persuade her to believe in him, despite his connection to Cabhan? Only together can the three cousins defeat their enemy. And Branna's feelings for Fin could hold the key ...