Lady of Conquest by Medeiros, Teresa

He is called Conn of the Hundred Battles, the warrior-king who forged a nation from a land of isolated clans. As High King of Ireland, he rides with the legendary Fianna, his elite band of warriors. But a threat to the throne looms from a mysterious scourge who has vanquished several of Conn’s bravest warriors. Conn rides out alone to face a seemingly invincible foe, never expecting that he will confront a grief-maddened hellcat with emerald eyes and hair like liquid flame….Wielding a sword called Vengeance, Gelina O Monaghan has sword to defeat the man she holds responsible for her family’s ruin. She never dreamed she’d be bested by him in combat…and lose her heart in the bargain. Their forbidden passion will become a private war fought with swords and kisses, promises and betrayal – and surrender will be only the beginning….