2147. The Mediterranean is a watery grave, swallowed by the rising tides. Humanity clings to life in Nymria, a city built within the bones of a drowned metropolis, its heart a breathtaking structure of bioluminescent coral and aquaglass: the Blue Cathedral. Survival hinges on the songs of the Singers, whose voices maintain the city's integrity against the crushing deep. Their music is life. Silence is death.

Emrin Taval, a Singer with a voice of terrifying power, is both revered and feared. Her songs hold a discordant edge, a tremor in the deep, scrutinized by the Council of Resonance who see her as both savior and destroyer. When unnatural tremors rock Nymria, Rhonda Hayes, a historian haunted by the lost surface world, recognizes the echoes of Thalassa, a forgotten oceanic entity whose imprisonment is tied to the Singers' melodies.

Together, Emrin and Rhonda plunge into the submerged ruins, uncovering a chilling truth: the Blue Cathedral isn't a haven, it’s a prison, the aquaglass its bars, and the songs, its lock. Joined by Ezra Blackwood, a reclusive engineer burdened by his family's secrets, they navigate a city fracturing under the weight of its secrets. The Harmonists cling to tradition, the Dissidents clamor for silence, while Emrin's uncontrolled power threatens to shatter the delicate balance holding Thalassa at bay.

As the city teeters on the brink of collapse, Emrin must confront her legacy, her power, and the terrifying truth of the songs. Can she find a new harmony, a language not of control but of coexistence, before Thalassa's rage consumes them all? Or will the blue cathedral become their tomb?