A charming fantasy set in an underwater world with magical academia and a heartwarming penpal romance, perfect for fans of  A Marvellous Light  and  Emily Wilde's Encylopaedia of Faeries.   “An underwater treasure-chest to be slowly unpacked, full of things I nosy and loving families, epistolary romance, gorgeous worldbuilding, and anxious scholars doing their best to meet the world with kindness and curiosity.”  —Freya Marske, author of  A Marvellous Light A beautiful discovery outside the window of her underwater home prompts the reclusive E. to begin a correspondence with renowned scholar Henerey Clel. The letters they share are filled with passion, at first for their mutual interests, and then, inevitably, for each other. Together, they uncover a mystery from the unknown depths, destined to transform the underwater world they both equally 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, are left to solve the mystery, piecing together the letters, sketches and field notes left behind—and learn what their siblings’ disappearance might mean for life as they know it.   Inspired, immersive, and full of heart, this charming epistolary tale is an adventure into the depths of a magical sea and the limits of the imagination from a marvelous debut voice. Praise for  A Letter to the Luminous Deep “A shimmering, delicately crafted delight.”  —H.G. Parry, author of  The Magician's Daughter “A fascinating and charming story told in a uniquely elegant voice.”  —Louisa Morgan, author of  A Secret History of Witches “Both the setting and the story are exquisite.”  —Megan Bannen, author of  The Undertaking of Hart and Mercy