An ancient Irish goddess appears to thirteen-year-old Colin Caulfield and delivers a fateful warning. Later that night, his sister is almost kidnapped by goblins. His world is rocked even further when his mother and a family friend reveal that he is the reincarnation of Ireland's greatest hero, CuChulainn, and destined to help the Irish gods return to their seat of power.
First, he needs to be properly trained, and there is no one better for that job than Scathach, the woman who trained the original CuChulainn. He arrives on her island, Alba, in the Otherworld, and joins her host of trainees. There, he meets Breccan and Alaynna, who become two of his best friends. He also meets Niall, who is somewhat hostile to him at first, but then agrees to help train him.
Colin faces a number of threats and challenges while on Alba, some of which are tied to a dark force that wants to stop him from fulfilling his destiny. Unfortunately, Colin's greatest enemy just might be himself as a deep-seated personal issue triggers a warp-spasm, a type of berserker rage that the original CuChulainn suffered from as well. With the help of his friends, Colin must learn to control the warp-spasms if he is to become the hero both Earther and the Otherworld need him to be.
He had better hurry though, because the dark force that wants to stop Colin, that found him on Earth and tried to use his sister to get to him, discover he is on Alba, and who knows how far they are willing to go to stop Colin this time.