A Letter to the Luminous Deep is an absolutely beautiful light academia cozy fantasy read. If you enjoyed Emily Wilde's Encyclopedia of Fairies or have ever wanted to read a book that feels like Palamedes and Dulcinea's letters from the Locked Tomb must, you will love this.

There is a beautiful epistolary romance that will make you swoon, as well as two queer protagonists, one of whom we also get to see fall in love. There is a lot of kindness and familial love. There is a mystery that at times did scare me a little and kept coming together beautifully. There is a lot of scholarly language that made me feel deeply immersed in the story and as if I was personally reading a report on some beautiful and fantastical mystery.

And very importantly to me personally, there is incredibly well done OCD representation that draws on the author's own experience. It is so rare to see OCD rep in fantasy and I loved and empathized with E. so deeply. I highly recommend you pick up this beautiful story and cannot wait to unravel the mystery of the luminous deep in book two.

Headlines:
A fantasy world under the sea
Two awkward people
Connections through letters

There's so much uniqueness in this story, this world under the sea, coral reefs, sea creatures and of course the societies inhabiting. The world seemed futuristic possibly to our world and vague references were made to a previous civilisations and possible climatic issues. That said, the world of this story was visceral, colourful and kept my imagination busy visualising.

The story was told in epistolary format, with a somewhat formal tone. That was a little jarring initally but I did settle into the format and the letters got more informal as time went on. There was a mystery afoot in this story, some missing main character and siblings of the missing E and Henerey also conversed through letters in their grief and search for answers. I did have to concentrate quite hard initally to be certain if this was a letter between E and Henerey or a letter between their respective siblings.

The characterisation authentically wove in some mental health issues with a rather anxious E and a contrast in the support and understanding or lack of she got from her siblings. Siblings on both sides were queer characters. For me, Henerey and E were a delight and while the sibling brought key parts to the story, I was always eager to be back with those two MCs.

I'll definitely be reading on, I need to know the what next. Will the next book be epistolary, I wonder? I can't see that it would need to be but who knows!

I both read this and listened on audio for larger parts and the narration was very good, assisting with the POV changes through voice.

Thank you to Orbit Books for the review copy.

This book was unusual, but in a very good way, I liked it a lot! It's an epistolary novel about siblings and couples, about loss, mental health and academia, set in a world where there is only very little land and most people live on (or in) the ocean.

Together with Sophy and Vyerin we discover the fates of their lost siblings, while reading their correspondence from before their disappearance. This plot structure worked very well for me, I was intrigued to find out what happened to them and at the same time loved to see their love and friendships respectively develop through the letters and notes they send each other. Usually I tend to miss direct conversations and actual meetings in epistolary novels, but this one managed to bring across all the important feelings and thoughts beautifully.

The writing itself was also amazing, there were various distinct voices transported in the letters and the characters really came to life through their writing. E. and Henerey have such a beautiful writing style, rather old-fashioned but in the best way! I really liked it.

The world was super interesting with all its different scholars and vessels and habitats and creatures! I can say that I've never read a book about a world like this and I thought it had the right amount of detail. Some scenes were a little difficult to imagine but that's also due to the epistolary form of this book I think.

Towards the end it was very gripping, though the last few letters were a bit anti climactic, but maybe that was just because I was so tired. Overall I'd recommend this book to everyone who likes to read epistolary novels and slow-ish fantasy set in a unique world.

Thanks to orbit and netgalley for the arc!

I found the book dragging for the first 60 or so pages, and was tempted to DNF due to the lack of progression, similarities in tone between every single character, and minimal world building... BUT after delving deeper, I found myself becoming enamored with the oddities and marvelous mysteries contained within the epistolary form.

Yes, this is a slow book. Yes, you will wonder if anything is ever going to actually happen. No, not everything concludes neatly (far from it, as this is just book one). Despite all this, A Letter to the Luminous Deep is well worth a read. I ended up loving having the secrets unravel letter by letter, and it allowed me to piece together what happened and what may happen in future alongside Sophy and Vy. In fact, I felt exceptionally clever when I thought I'd uncovered what the Structure was only to then have its true nature be even more wonderous. It's not often a book truly surprises me, so I was thrilled by the eventual realizations and the plan to seek out answers.

The storyline is intricately crafted, with hints dropped from the very start so you can look back and collect the evidence much like a Boundless Scholar. The prose varies from twee to poetic, making the characters and their aquatic world slowly come to life as you warm up to their written words.

Even the romances were charming. From courting in the depths to a love that grew from a single letter penned with anxiety and heartfelt appreciation... There is a relationship for everyone to admire here.

While E and Henerey do not have much in the way of face to face interactions, what they share on paper creates a deep level of trust and mutual respect that blossoms into something more. I do hope the next book allows for verbal communication as I would love to see these two working together more!

Overall, A Letter to the Luminous Deep is mysterious and magical (albeit slow to start), and will be a treat for those who like underwater adventures, academia, and a focus on mental health.

I have mixed feelings on this book - and I'll start with the positives!

Firstly, both E and Henery were very compellingly sweet characters, and my favourite parts of the book were reading their exchanges. I wish there had been more of their letters.

Secondly, I found the format of reading a book entirely composed of letters / notes to be an interesting one, and in some respects enjoyed this slow unravelling of this fantasy world and tale.

The downside to this format, especially in reading a fantasy novel that requires world building, is that as this was done through letters - it felt a bit disjointed, and I found myself often confused and not following completely. I actually almost stopped reading at some points as it was almost too complicated as a reading format. I think also as it was building a fantasy world, and the characters all had unusual made up names - and even the measures of time were not 'normal' - added to this confusion.

With all of that being said, I am glad I made it to the end to see what potentially became of E & Henery, and appreciate the complexity of writing such a book in this format!

Many thanks to Little Brown Book Group UK | Orbit, Sylvie Cathrall & NetGalley for an advanced reader copy in exchange for my review.

A Letter to the Luminous Deep sounded right up my street. I loved the title and couldn’t wait to read it. I love fantasy so this book ticked all of the boxes for me. I loved this book, really loved it. Everything about this book delighted me. I didn’t want to stop reading it and leave the world and characters behind. The really liked the way the book is structured, a series of letters between characters as well as journals, newspaper articles etc. I’ve never read a book that uses this structure before so it took me a while to get into. I also like books that use time shifts so I had a great time reading this. I loved it and would recommend it.

Thank you to NetGalley and Little, Brown Book Group for providing me with an eARC of this book!

A Letter to the Luminous Deep was one of my most anticipated reads for this year. At first glance, it hits all of my most favorites. Beautiful prose? Check. An academic (or academic-adjacent) setting? Check. A quirky/misunderstood FMC and a soft and loving MMC? Check.

Separately, I enjoyed pretty much everything about this book. But the actual execution and combination of ingredients just fell flat.

I really enjoyed the POV characters, both E and Henerey and Sophy and Vyerin. I thought they felt well-developed and were interesting.

I also really enjoyed the world and the world-building. I am a huge fan of the ocean and aquatic life. The world this book was written in did very much intrigue me.

And the plot (what bits of it we had) also did interest me. I am curious about what happens next. Admittedly though, I had no idea this was not a standalone work and I wish I had known as it might have tempered my expectations for plot delivery.

But as I said, despite enjoyable ingredients, the final product just didn’t hit the mark for me. If dragged for much of the book, and many of the entries felt as if they were just fluff rather than actual advancement.

This was a beautiful book. I wish I had liked it more.

A Letter to the Luminous Deep by Sylvie Cathrall
2/5 stars
I loved the idea and format of the book but I found that I struggled to fully get into the book. The cover is absolutely stunning and I really wanted to fall in love with this book which sadly was not the case.

3.5 stars (rounding up coz I want the ARC for the sequel when it’s available)
One Liner: Ultra-slow-motion; but beautiful!

E. sends a letter to renowned scholar Henerey Clel after she spies an intriguing aquatic animal outside her window. Soon, they correspond regularly and fall in love. However, life in the underwater world has its risks. When the duo uncovered a mystery, they didn’t know it could destroy E.’s home. E. and Henerey vanish, presumed dead.
A year later, E.’s sister Sophy begins to archive her articles. She contacts Henerey’s brother Vyerin, and they begin to go through the letters and notes to discover more about their siblings and the mystery.
What happened and why? How does the truth change their lives?
The story comes in the form of letters, news reports, and other snippets shared by different characters.

My Thoughts:
Firstly, a huge thanks to an early reviewer. It helped me go into the book with the right expectations (ultra-slow pacing, almost non-existent plot, and a cliffhanger). I’m sure I enjoyed the book more because I knew what it was going to be.
The beginning is intriguing but soon dissolves into a lengthy character-building exercise. While the idea of showing character development only through letters and journal entries is a great idea, it cannot come at the cost of the plot.
I continued to read and read and read and finally, after 70%, saw a ray of hope. Maybe if the letters were shuffled to provide two tracks – one to get to know the characters and another to follow the mystery, we might feel better involved in the book.
The underwater setting is ambitious. It takes time to understand the whole thing, so wing it until you get a hang of it. There are enough details to picture the setting, so it shouldn’t be too much of an issue. Moreover, the technology and stuff used can be compared to what we have, making it even easier to create parallels.
There’s no denying E.’s arc. It is indeed beautifully done. Sophy and others are well done, too, but E. shines just as she should. Henerey is equally adorable. My only grouse is that the plot and pacing needed to be sacrificed for this.
The letters are formal, with many post scripts, dashes, and parentheses. Do I mind it? Nope! That’s how they are supposed to write. It aligns with their professions and backstories. However, I wish the voices were a little more distinct. Giving them each a quirky trait might have helped. On a side note, I have no idea how this would work on audio.
The last section is truly where things start to come together. But it shouldn’t have been left until that point. Strengthening the threads from the midpoint would have worked even better.
Also, sorry, but E. Cidnosin sounds a bit too close to e coli (at least to my brain). It’s a me thing, but I had to mention it. Her full name, though! Poor girl. I understand why she preferred E.

To summarize, A Letter to the Luminous Deep is a character-driven book that sets the stage for the next book while providing snippets of information. Whatever is revealed is my kinda stuff, so I would love to read the next book and see where it goes.
Thank you, NetGalley and Little Brown Group (Orbit), for eARC. This review is voluntary and contains my honest opinion about the book.

Not a book for everyone - it is definitely one of these very polarizing works, but has indeed potential if you are that kind of reader.
The epistolary format, especially when paired with a descriptive, borderline poetic writing style and the lack of explicit action can feel slow paced and can create a disconnect between the reader, the characters and the story line. If the above is not a deterrent, you should definitely give it a try - a scholarly correspondence in a submerged world, a sprinkle of mystery and tender romance all unfolding via letters, articles and diaries entries could be exactly the right mix for that relaxing weekend where you long to get a glimpse of a different place while still sitting on your favorite couch. To me, this was not an “all in” page turner, but more or a gentle, whispered story observed from afar.

3.5 stars.

I've seen this compared to Emily Wilde and I understand the comparison because of the academic context and writing, sober yet moving romance, peculiar characteristics of the characters, and otherworldly mystery. That said, I enjoyed this, but I don't think it's as enjoyable as Emily Wilde and it doesn't have the same whimsy.

This is an epistolary novel, which is what attracted me to the book in the first place. I loooove a good penpal situation and it delivers on that front. I enjoyed getting to know all the characters and the letter exchanges made this very easy to get into and read. The writing style is academic, but it doesn't make things dense. Also, the worldbuilding is very interesting and I loved the underwater setting.

However, I do have a few issues. For one, I don't think this book needed to be over 400 pages long. It dragged on a bit and not much happens for most of it, so that dragging is not justified at all. I skimmed and I didn't miss a thing. This would've been great at, like, 300 pages, and I think a lot of things could've been cut without affecting the larger picture at all.

Also, the characters don't have distinctive voices. If you showed me an unidentified letter from E., another one from Henerey, and one from Vyerin, I would say it's the same person. All characters have different characteristics and I do feel like I know them, I just wish they felt different in their letters because they all express themselves exactly the same way.

Overall, I enjoyed this and I will be waiting for part 2 because I did connect with the characters and I definitely want to know how things wrap up. It was charming and interesting enough, cozy, and made me crave a penpal relationship.

A letter to the luminous deep

“Reading your letter was an experience like no other. Have you ever considered, E., that someone ought to write a Fantasy about you?”

A letter to the luminous deep was a UFO (Unidentified Floating Object) to me, and I mean that in the best of ways. Everything in it surprised, unsettled, passionated me. If you asked me to put this story in a box, I’d have a lot of difficulties. You’ll find a fantasy underwater world full of bioluminescence, a lot of scholars, some romance, a mystery, etc… I wouldn’t say one part takes the lead on the other, making the story very balanced.
The whole book is constructed around correspondence. We follow several epistolary relationships, in –mostly– two points in time. Besides the letters exchanged, we can also read bits and pieces of journals, newspaper’s articles, books’ abstracts, etc. That’s for the form, and I truly enjoyed that.
The back and forth with time isn’t a problem at all, as we discover E. and Henery’s story (and the circumstances behind their mysterious disappearance) more or less at the same time as their siblings. The other letters and “documents” are a very clever way to make the story progress seamlessly. It was also a great opportunity for character building. The characters are very lovable (E. !!!), and express diversity (neurodivergence –even if no true label is put– and LGBT+ especially).
The form also allows the author to build the fantasy world with a lot of subtlety. I found the reading very immersive, and experienced a lot of synesthesia in the manner the places and actions were described.
I would say the first ⅔ are slow paced, which for me was very enjoyable as it’s how I like fantasy books. The last third, though, as the mystery begins to really unfold, is a torrent of information and quite a page turner. I was surprised by the “political” turn of events, about how the scholar system and the environmental problems (and so on) are handled here, and I can’t wait to learn more about this whole world in the second book. (I didn’t know this was a series until the end of the book, but the end remains a satisfying one in itself.)
Thank you NetGalley, Sylvie Cathrall and Orbit book for that wonderful ARC!

One of those books where the concept is so cool I'm genuinely sad that I ended up finding it a medium reading experience all in all. I wish I loved it I really do

First things first: I really enjoyed the setting and general worldbuilding. A world that (almost) only consists of ocean is simply SO cool and I loved the Deep House, literal goals. I loved all the sea creatures that were described and the way humans have organised themselves in this aquatic world. Sophy's experiences meant we got more of how the Scholars operate than if it had just been E. and she was a nice addition (as was her exploration of the Ridge and everything related to that). I'm really intrigued by the history of the world and am excited to discover more about the mysterious Dive.

The characters were also really fun! Building real-feeling characters exclusively through letters is a feat and yet I found myself incredibly attached to both sibling duos (also big shoutout to this book for revolving so much about siblings. It's a type of relationship I always love reading about and it was done very well here). I also thought E's struggles with her Brain (a capitalisation she uses and I find highly relatable honestly- sometimes your Brain is a Person and Against You) were depicted really well. It was nice to read a book about a character who struggles with mental health without it being the whole point while it was still important to her experiences.

The characters do bring me to my first point of critique: although they were distinct in personality, they all sounded the same on paper. Not only did this make it hard to distinguish between them, but they were also all incredibly verbose, to the point that I sometimes struggled to understand what they were actually saying (especially frustrating when it came to the description of the Structure. I would have had no clue what it looked like without the illustration). I also found the plot not super engaging- although the letters were fun to read it felt like I was reading a prologue to the actual adventure that started at the end of this book. I think it would have been much more exciting to just fall face first into whatever happens next and then get the letters for context throughout the book. With just the letters, I was a little bored at times.

I will probably read the next book in the series. I'm honestly very attached to these characters now and I want to know wtf is going on!! It just feels unnecessary to have had to read this one too.

I received an ARC from Netgalley in return for an honest review.

I am trying to read more books out of my normal range and was thinking this could be a good start. However, I unfortunately couldn’t finish it. I stopped at about 40% in as I just could not see myself finishing it, and just couldn’t force myself to do it. It holds a lot of potential for sure, many people will enjoy the epistolary aspect and mysterious aspect as well. However, even if I expected cozy read, it just didn’t do it for me unfortunately. I will still recommend it to my store as I know many people would definitely enjoy it, it just was not for me.

It is an epistolary novel full of beautiful writing and a unique underwater setting following 2 scholars, living in separate pressurized vessels under the sea, who fall in love while solving an underwater mystery through letters.

I liked the FMC, E; I felt the same kinship that I felt with Emily in Emily Wilde's Encyclopaedia of Faeries, they are both very clever, introverted, and quirky; however, that's where the similarities start and end with the two books.

The entire book is written in various forms of correspondence and is very formal, making the tone and voice of each character difficult to differentiate. The formal writing makes for a very long hard read and there is, in my opinion, a lot of fluff, and nothing exciting happens until the book is nearly over,

The world-building was very good and the descriptions made it very easy to imagine the underwater setting.
I wanted to love this book especially as it's so pretty and the premise very promising; however, I almost DNF'd at so many points in the book.

A Letter to the Luminous Deep is written in letters and set in a mystical underwater fantasy world. It tells the story of reclusive E and Henerey Clel who fall in love through their letters. When a seaquake destroys E.'s home, both E. and Henerey disappear. A year later, E's sister Sophy and Henerey's brother Vyerin try and solve the mystery behind their disappearance through their letters, sketches, journals, and field notes.
A slow burning but magical, fantasy read with the most stunning cover.

I found this book quite difficult to read. The format, an epistolary novel, was intriguing to me, but I unfortunately found that it had trouble making every character sound "distinct", and it was often difficult to discern which character was speaking.
The concept of this book, however, as someone who has been in a pen-pal or long distance relationship was really interesting to me, and I found that that was really nice.

I enjoyed watching the relationships develop, thought the worldbuilding was super interesting and was curious about a lot of things while I read this, but I simultaneously found the format and the prose to be not quite my thing.

I think this book is great if you love in depth explanations and worldbuilding in the form of letters, scholarly style of writing, and if you are interested in the format!

I was really intrigued by this premise, a story told through letters, scholars, underwater societies, and two lovers that go missing. However, the beginning felt slow, the mystery didn't feel urgent, and the characters that were supposedly trying to find them mainly spoke about their families and their lives under the sea for a lot of the book.
I though the writing was beautiful, I enjoyed hearing about the characters, but I would have liked more focus on the mystery aspect. A very unique way to tell a story, but ultimately, the story lacked a little something for me.

In a submarine world wrought with mysteries, two sets of correspondence draw the outlines of new friendships and potential love in the wake of grief.
I think the best adjective to define this book would be “charming”. It feels very quaint and old-fashioned in a good way, and highlights the best parts of its characters — their unshakable faith in the fact that there’s some good in this world, Mr Frodo. All of the characters (we follow four epistolary writers) are very endearing and kind-hearted.
I haven’t read lots of epistolary novels (mostly classics) but with a generous suspension of disbelief it worked really well. There were some parts that felt a bit repetitive, but it’s easy to blame them on the characters’ anxiety and desperate need to be understood. I did wish we as readers learnt more about the worlds, but it would make zero sense for characters to start explaining things they know to each other. The trick of having one character living in isolation enabled the author to get the necessary elements to the readers fluidly.
I loved the atmosphere of curiosity and research that pervaded the book. I think it’s the first “light academia” book I’ve read, but I have no doubt it belongs to that subgenre. I would have enjoyed a little darkness myself, to balance the pastels and fluffiness, but I understand it was not the place for it. Well, not all of it is cheerful since we know from the start that two of the correspondents are dead. But believe me when I say the author handles that fact with the utmost delicacy and though you might find your heart wringing at times, it really is a cute story.
Rep: MC with OCD and possibly demisexual, sapphic MC, bi MC, MC with social anxiety.
CW: underwater scenes, confinement, grief.

A Letter to the Luminous Deep by Sylvie Cathrall, with it's oh so beautiful cover, is a charming, romantic and character driven story set in a scholarly underwater world.

I was initially a little daunted that it is an epistolary novel - told entirely in letters - but I needn't have worried, for the writing and well drawn characters soon draw you into the story until you are immersed in this well crafted tale.

The characters, with all their foibles, are charming and delightful and their letters are heartfelt and engaging. A discovery outside the window of her underwater home, the Deep House, prompts the anxious and reclusive E. to begin a correspondence with renowned scholar Henerey Clel. As their relationship grows they uncover a mystery from the unknown depths that could transform their world. But when they disappear in a seaquake it is left to E's sister Sophy and Henerey's brother Vyerin to attempt to solve the mystery of their disappearance using the letters, sketches and field notes they left behind. We get to peek at different facets of their characters in the letters they wrote to the different people in their lives in what is a formal and very academic society beneath the waves.

It reads rather like a classic novel and the slow burn and lovely blossoming relationship between the two socially awkward main characters is pieced together by their siblings who in turn forge their own wonderful friendship in the process. I was wholly absorbed in the tale and fully rooting for the endearing characters. Representation was excellent too.

The book is slow burn in terms of plot as well as the relationships, as the world building and the mystery at its heart gradually unfolds and sets the scene for the next book in the series. I really enjoyed reading this novel despite not being wholly satisfied with the ending, but I will undoubtedly be picking up the next book and am intrigued as to where it's mysteries will lead.

4.5 stars - perfect for fans of gentle, cozy fantasy.

A Letter to the Luminous Deep publishes in the UK on 25th April. Many thanks to Netgalley and Orbit Books UK, part of the Little, Brown Book Group, for providing me with a copy of this book to review.