The Fomorians lost at Mag Tuired. Everyone knows that story.But Nessa Dowd can hear what the water remembers, and the water is not done.Something old has moved under Corryvreckan — older than Balor, smaller than legend, and far more dangerous for having hidden beneath a famous name. It is not a return. It is an echo. And echoes carry the shape of what made them.With Finn, April, Jack, and the rest of a team still marked by the last fight, Nessa follows the signal north — into the Gulf, through a city where ink moves on its own, and toward a name so old it has survived by refusing to be written down.