'An underwater treasure-chest to be slowly unpacked, full of things I adore: 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 LightA 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 Encyclopaedia of Faeries.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 of their siblings' disappearances with the letters, sketches and field notes left behind. As they uncover the wondrous love their siblings shared, Sophy and Vyerin learn the key to their disappearance - and what it could mean for life as they know it.Praise for Sylvie Cathrall:'With its gorgeous underwater setting and whimsical academic sensibility, A Letter to the Luminous Deep is a strange, epistolary wonder.' Mary McMyne, author of The Book of Gothel'A shimmering, delicately crafted delight. . . Readers looking for heart warming romance and scholarly mystery against the backdrop of a wildly imaginative world will be charmed' H.G. Parry, author of The Magician's Daughter'Cathrall's debut caught me up on a wave of whimsy and swept me away with its charm. A story to be cherished' Lyra Selene, author of A Feather So Black'A Letter to the Luminous Deep is a fascinating and charming story told in a uniquely elegant voice. A watery wonder of a novel! I loved it.' Louisa Morgan, author of A Secret History of Witches 'A Letter to the Luminous Deep is like nothing I've read before. The heartfelt intimacy of the epistolary narrative, juxtaposed with the magnificent oceanic world-building, results in a novel that is at once deeply human and mind-bogglingly imaginative. Both the setting and the story are exquisite, but it was the lovingly crafted voices of the characters that kept me hooked from beginning to end' Megan Bannen, author of The Undertaking of Hart and Mercy