The seals are breaking. The ancient patterns are failing. And the power spreading through her may be the key to salvation. Ellie thought finding her vanished mentor would bring answers. Instead, she discovers Zaren has been hunting something far more dangerous than the Servants—an artifact that could either repair the failing barriers between worlds or shatter them completely. From the haunted port of Saltmere to the lawless Whispering Coast, Ellie races against servants of the Quell who use her own corruption to track her. Every seal that fails brings the Quell closer to breaking through. Every use of her opposing powers tears her further apart. And in the spaces where the separation of realms grows thin, something vast and hungry watches her progress with terrible patience. To save both worlds, Ellie must become something a bridge between realms, a wielder of impossible harmonies, and perhaps the last person who can restore the First Song before the boundaries collapse forever. Old debts are calling. Ancient powers are stirring. And the key to everything might already have been lost.