Aqua Magic

Brenna Ross is trapped in her own mind. Possessed by a Marwolaeth, that is slowly killing her, it used her to murder those she loves. As hard as she struggles to regain control of her body, she can't break free. Still she will fight, desperately trying to tell her sister she's sorry.
Marcus Ondine knew the minute the little witch and her older sister walked into his pub, The Blue Dolphin, she was "the one" — what the magical folk call his "Destined One." Now he's returned to Earth to find her possessed by the Marwolaeth. Only by taking her to his home world of Aquarias can he save her from death, but what will happen when she wakes and finds herself in an underwater world?