Sweetly Shining: A Letter to the Luminous Deep by Sylvie Cathrall

Posted 19th April 2024 by Sia in Queer Lit, Reviews, Sci-Fi Reviews / 2 Comments

A Letter to the Luminous Deep by Sylvie Cathrall
Genres: Queer Protagonists, Sci Fi
Representation: MC with clinical anxiety, possibly ace-spectrum MC, sapphic MC, MLM MC, background F/F and M/M, queernorm world
PoV: First-person, present-tense; multiple PoVs
Published on: 23rd April 2024
ISBN: 9780356521091

Dive into the curious correspondence of Sylvie Cathrall’s delightful debut novel, A Letter to the Luminous Deep.

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.

Perfect for fans of A Marvellous Light and TJ Klune, A Letter to the Luminous Deep is a whimsical epistolary fantasy set in a mystical underwater world with mystery and heart-warming romance.

I received this book for free from the publisher via NetGalley in exchange for an honest review. This does not affect my opinion of the book or the content of my review.


~an underwater house
~an archipelago in the sky
~mysterious eels
~academia politics
~a love letter to questions

You know the craving you get for books that make the inside of your head go quiet? The kind that softly, gently make the world around you disappear, so all there is is the story? A story which is like cashmere wrapped around your brain, a story which is never boring but also never…never stressful? One that never feels like work to read, that manages to be pure, warm escapism like a mug of your favourite hot chocolate?

Hi, let me introduce you to A Letter to the Luminous Deep.

The title is apt in more ways than one, and I decided to use that as the framework for this review. Thus!

Reason the First

The first reason the title of this tale is so perfect is that the book is literally made up of letters (…not the alphabet kind)(I mean, obviously those too!) as the style is epistolary, each chapter comprised of missives and notes passed between E and Henerey, and between E’s sister and Henerey’s brother, with the occasional interjection of letters and reports from others, like E’s brother or honorary aunt. I happen to really love epistolary stories, but I think that even if you don’t, Luminous Deep is likely to convert you; and if you’ve never read an epistolary novel before, then this is a pretty excellent introduction to the form. Each character has a very distinctive voice (vitally important when all we have is their first-person communications!), and each missive is clearly marked with sender, receiver, and date, making it very easy to keep track of who’s talking to whom and when. And though I do not think first-person is a guaranteed way to make the reader feel more connected to the character/s, Cathrall made me feel like I was a part of the conversation the characters were having, not a witness to it but participating in it, and that’s not a common writerly magic!

It doesn’t hurt that the cast is packed full of lovely people that I loved getting to know. E has intense clinical anxiety and has been a shut-in for years, but she’s very brave (even if she doesn’t think so) and fiercely curious about the world around her (one of my favourite character traits, in real and fictional people both): she kickstarts the whole story by writing to a naturalist – Henerey – about a sea creature she’s seen that might not yet be known to science! Henerey proves to have been a good choice to write to, as he’s a wildly enthusiastic sweetheart, who’s not very socially adept but is more than smart enough to see how wonderful E is, which would earn him major points with me even if he wasn’t also the human equivalent of an excited, lovable puppy.

Alongside these two are our other main characters; Sophy, E’s sister, and Vyerin, Henerey’s brother. The conceit of Luminous Deep is that, a year after E and Henerey mysteriously vanish, Sophy and Vyerin get in touch to try and figure out what happened, sharing with each other the correspondence their respective sibling sent to the other’s. The two timelines are completely interwoven; Sophy and Vyerin communicate back and forth in the same chapters as E and Henerey do, so that a quick note to Sophy often directly follows one of Henerey’s long letters to E. In the hands of a lesser writer, this could have been confusing or messy, but happily it was nothing of the kind, and Sophy in particular became very dear to me. She’s much more vivacious and outgoing than her sister, whereas Vyerin is a little more withdrawn (at least until he gets to know Sophy better) but feels things just as intensely, even if he isn’t always able to commit them to paper. Sophy also has her own story going on while Henerey and E were communicating; a scientific endeavour during which she met her now-wife, and during which she and E often exchanged letters too. Henerey and E’s developing friendship, then near-romance, is charming and delightful; Sophy’s adventure is fascinating, but also anchored in emotion and human relationships, which I appreciated.

(There’s also E and Sophy’s brother, who is a bit of an ass, but luckily we don’t have to deal with him very often.)

Reason the Second

As for the second reason as to why the title is so appropriate; not only is this a book written in the form of letters, the vast majority of those letters are going down into the depths of the ocean. E lives in Deep House, a large and cosy one-of-a-kind home on the sea floor designed by her (now-deceased) mother. It is not, however, at the bottom of any of our oceans.

I wasn’t sure what to expect re the setting, going into this book, but Cathrall has created an entirely new, separate planet for her debut; a world that is almost entirely covered in water, with very little natural land accentuated by a handful of artificial islands, and a fair few communes built or lashed together that float along on the ocean surface. That already makes for an interesting set-up, but what made my jaw drop was learning that humans aren’t native to this world at all.

Hi, I love this??? The reveal that humans came from elsewhere is a blink-and-you’ll-miss-it moment – it’s really not relevant to the plot, or the characters’ lives, at all – but it’s the kind of detail that just makes me light up. And it does help explain how the society of this world is the way it is, and it’s the kind of thing that might be very relevant indeed further down the line – my personal theory is that the big mystery E and Henerey uncover is Not Unrelated. But that you’ll have to read about for yourself, because that definitely would be a spoiler.

A not-insignificant number of letters go deeper still into the waters – more Depths! – following Sophy while she is part of a scientific team exploring something similar to the Marianas Trench of our world. It’s the deepest humanity has ever gone in this world’s oceans – a Very Big Deal indeed! – but thankfully, Cathrall declines to write this plotline like some kind of The Meg (2018) nonsense; far from being some kind of thriller-horror mess, this, like the E-and-Henerey storyline, is quiet, almost cosy, focused on the interactions, emotions, and developing relationships between the different Scholars (as this world names its scientists) as well as the sheer joy of scientific discovery.

Which segues nicely into…

Reason the Third

I’ve often seen (and you probably have too) artworks called ‘letters’ or ‘love-letters’ to different topics or themes. And that’s the third way in which this book’s title is perfect for it, because Letters to the Luminous Deep is in itself a letter – a love-letter to wonder and curiosity, questioning and discovery, to diving into the depths of the unexplored or unexplained or even completely unknown, and celebrating the urge to learn, learn and share what has been learned. This is a love story, yes, but not only because what E and Henerey have becomes a romance, or because of the wife-to-be Sophy meets in the darkest part of the ocean – it’s a love story because it is a story about the love of learning. That’s what brings E and Henerey together; it’s what brings Sophy and Niea together; and it’s woven into every page of the book. Luminous Deep fairly glows with it – pun unintended.

I don’t know if I’ve seen that before – a book that celebrates curiosity and the yearning to know and the delight of discovery. I can’t think of another example, and that’s sad, because these are qualities, concepts, things that we should celebrate, and that I would love to see more often in my sci fi. I feel like this should be a foundational aspect of science fiction, actually, now that I think about it – every piece of sci fi is fundamentally an answer to someone’s what if?, is it not? Then what could be better, or more natural, or more correct, than science fiction that is not just an answer to someone’s what if?, but also encourages the audience to ask their own questions? Not just of that particular piece of art, but of the whole world?

Which is to say: this is a warm, lovely book that will not hurt you, that manages to be soft even when it is a little bit scary, that is charming and fun and wonderfully readable. It is not action-packed; there is not even much in the way of actual plot for at least the first half of the book. And it would be enough – more than enough! – to ‘just’ be soft and sweet. We need more of that in the world.

But Letters to the Luminous Deep manages to be soft and sweet, and to celebrate and encourage curiosity and learning. Which I think makes it something very special.

Honestly, I think it’s utterly perfect, and you’ll be seriously missing out if you give this one a skip.

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2 responses to “Sweetly Shining: A Letter to the Luminous Deep by Sylvie Cathrall

  1. Wow, this book is pushing so many of my buttons: scholarship fantasy, living underwater, unravelling mysteries through letters, siblings, gentle plots, Bigger Things Possibly Afoot Than We Know. My TBR pile just sucked this one in like the old friend we never knew we had!

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