A beautiful discovery outside the window of her underwater home prompts E. to begin a correspondence with scholar Henerey Clel. Their letters are initially filled with passion for their mutual interests, and then, inevitably, for each other. They uncover a mystery that will transform the underwater world they both fear and love. But by no mere coincidence, a seaquake destroys E.'s home, and she and Henerey vanish. A year later, E's sister Sophy, and Henerey's brother Vyerin must solve the mystery by piecing together letters, sketches and field notes left behind --- learning what their siblings disappearance may mean for life as they know it.