For eighteen years, the world has known peace. But the shadows of the past are stirring. Four young rulers, raised in isolation, are summoned by the gods. They are the children of the legendary king Seoighe mac Danu, born of a love forged in the wake of his victory over the dark god Crom Cruach. Now, they must unite to face a new darkness. Cináed, a former disciple of their father, has been corrupted by the very power Seoighe sought to contain. He seeks to resurrect Crom Cruach using seven dark idols, and he has already found five. The fate of the world rests on the four siblings, who must become the Threshold—a unified force of fire, water, air, and earth—to stop him. But they are strangers, divided by their different upbringings and the weight of their shared legacy. They must learn to trust each other, to master their powers, and to become the heroes their world needs. For if they fail, the darkness will consume everything. The Shadow of the Threshold is a sweeping epic of magic, myth, and the enduring power of family. It is a story of a new generation of heroes, who must rise to the challenge of their legendary father and forge their own destiny.