In fifth-century Ireland, a young prince named Conor is thrust into the role of leading a group of rebels against the invading Romans after most of his family is massacred. First, however, Conor faces the daunting task of uniting all the warring Celtic tribes. Helping him are his mentor, Fergus; Tully, an apprentice magician; and Caitlin, a runaway slave. Their chief foe is Longinus, a sorcerer who is actually a 400-year-old centurion who is under a curse for piercing the side of Christ with his spear. His lover is Diana, the power-hungry Roman queen.