The White Mare The Dalraida Trilogy, Book One

It is 79 A.D., and the tribes of Scotland are among the last holdouts to the Roman conquest of Britain. Unaware of the perils that face them, embroiled in internecine squabbles, they will soon be faced with a grave choice: band together or become slaves. Rhiann, a Scottish priestess and princess, is forced into a marriage arranged to promote a strategic alliance. Scarred by a horrific past, she desperately looks for a way out, but sees only the Romans closing in. Into this volatile situation sails an Irish prince, Eremon, exiled from his home by familial treachery. His aim is to win renown and regain his throne, but first he has to deal with an unexpected alliance, prove himself a military leader, and unite the feuding tribes of his adopted country.