A Prelude to War
Conaire is made high king because the Elder Council want a peaceful kingdom. They fear invasion by the horde from the south, the Romans, but their manipulations weaken the Five Kingdoms and war does come to Ireland, but from an unexpected place. The Five Kingdoms are saved by the Red Branch warriors, but not before The Peaceful King is killed by the invaders.
When Conaire is killed, the Five Kingdoms are in turmoil. Conor Mac Nessa, king of The Ulaid, tries everything in his repertoire of evil skills to gain the high kingship but he is opposed by Queen Medb, the Warrior Queen of Connacht.
Their rivalry gives birth to a hero, The Hound of Ulster.