what a magical debut book this was with stunning writing and characters who have become so very dear to me!

i went into a letter to the luminous deep not knowing much except that it was an epistolary set underwater, and i'm delighted that i adore it so much (i think i started this at the perfect time too, although i also cannot believe i've left it sitting in my tbr for so long all this time (but better late than never))! with every page i turn i was fully immersed and felt like i was a part of this project with sophy cidnorghe and vyerin clel, all the while dearest e. cidnosin and henery clel embedded themselves deep in my heart. there were exchanges between these characters that were just absolutely precious and so silly argh!!! the cutesie patootsies!!!! i had the coziest sweetest most magical time reading this and i will be eagerly anticipating sylvie cathrall's next works that she has in store.

a biggest thank you to the author and the team for providing an ARC.

Let me start by saying that I love the premise of this book. A light academia set on a watery world featuring a slow, slow burn romance between a agoraphobe living in an underwater architectural wonder and a socially awkward academic prodigy? Perfect. Epistolary novel? Yes, please. The book was exactly what I expected, and I quite enjoyed the whole experience. My main gripe is that there were a lot of world-building details that just didn't seem as well-developed as I would have liked. This is almost always going to be the case in an epistolary novel, but with the really interesting premise of the world, I wish that it had been better developed. The timelines for the letters was sometimes off-putting, but not really an impediment to reading. The real difficulty with this book? The letters were (intentionally, I think) way too over-written. Is that how my brain thinks? Often, yes. But it was often a bit too difficult to read all of the parentheticals and paragraph-length sentences. The story was quite enjoyable, and I enjoyed both the mystery and the romance, but some of the reading experience was a bit difficult with the structure of the prose.

this is an epistolary novel that follows correspondence between a recluse and a renowned scholar, told through their siblings as they try to uncover the mystery behind their disappearance. the premise and prose of this book really hooked me, and the different kinds of character relationships were very well executed. this book only started to lose me nearer to the end, where some of the mystery is explicitly explained.

I DNF’d 10 pages in. The writing was obtuse and hard to understand and I hated the letter format. Disappointing for such a pretty book.

Took me a bit to get into, and it wasn’t until pretty late in the book it all started to come together. Now it makes sense why there will be more books. It was also an interesting approach with the epistolary format (though too many exclamation marks!). I will very likely continue the series.

This book won me over, page by page. I didn't really know what to expect aside from it being an epistolary novel, which I haven't read many of. The start was a tad slow going, for me, as I got the hang of each POV and their personalities. The more their environments, passions and relationships were discussed, the more I was invested and ultimately hooked. This entire story felt unique to me; from the underwater living, family histories, to the childhood nightmares and fantasies.
The mysterious disappearance and end reveal has me upset that book 2 isn't out yet.

Thanks to Orbit and NetGalley for the eARC!

What is the opposite of Dark Academia? Bright Academia? Radiant Academia? Whatever it is, Letters from the Luminous Deep certainly qualifies. This cozy, epistolary fantasy features a slow blooming romance and an intriguing mystery.

The world in this novel is predominantly aquatic with only a small landmass being available to humans. People either live on ships, in buildings underwater or on man made islands. Our heroine E (her full name isn’t revealed until the end) lives in an architectural marvel called Deep House, where she is somewhat of a recluse. Based on her descriptions of herself, she suffers from anxiety and OCD and prefers her underwater home to society.


One day E sees two unusual eels and sends a letter about them to Henerey Clel, a Scholar whose expertise is something similar to Linnaean classification of species. Henerey has never heard of this variety of eel, and the two begin a correspondence that ignites a friendship and eventually a long distance love affair.

The reader gets E and Henerey’s correspondence as well as something similar to email between E’s sister Sophy and Henerey’s brother Vyerin. It’s through the latter that we learn that E and Henerey have gone missing in a disaster involving Deep House.

There’s so much to love about this novel. The world building was unfolded within the epistolary storytelling, as did the slow-building elements of romance and mystery. I would describe this world as almost an aquatic Victorian realm at the height of the Age of Discovery. Exploration and science are all the rage, but it’s also a proper and mannered world (at least E and Henerey’s class is). There is a formality to the letters that make this feel like historical fantasy.

E and Henerey are both a little bit awkward, and their romance is incredibly sweet. Henerey makes an effort to be understanding of E’s anxieties and to never make her uncomfortable. Even though the reader never “sees” the couple together in real time—rather through their own memories captured in writing—their blooming love feels at once very gentle and urgent at the same time.


The only thing I didn’t like about this book—and it’s not really a complaint—is that it ends on a cliffhanger and we have to wait until the next installment to find out what happened to E and Henerey.

If you are looking for a cozy fantasy read with excellent romance and worldbuilding, I highly recommend Letters from the Luminous Deep.

I'd like to thank the publisher and NetGalley for allowing me a chance at reading this.

I've read stories which involve two characters conversing via letters (84 Charing Cross Rd?) but that one felt like it was to the point, apt, and got the message of friendship across.

The letters expressed in this were - to me - boring and confusing, the characters who were relaying the letters back and forth to one another (the siblings who are looking for the letter writers) seemed to be a bit more interesting, and honestly, I wished at times were got plot with them where we got to see them OUTSIDE of the letters back to one another.

Cozy romantasy / fiction is on the rise, and I don't think I'm a person meant for it.

This was a sweet, slow paced novel that tested my patience. I loved lazily exploring this oceanic world through the letters between two strangers and their siblings. I wish it had been a bit more fast paced, but that may have just been a mood I was in.

I tried to read this, twice. Both unsuccessful. Something about the writing felt like blocking me out🥲 i couldn’t connect with the story at all. Quite disappointing since this was marketed to be perfect for Emily Wilde’s fans…

Thank you to Orbit and NetGalley for providing me with an eARC!

Let’s start off by saying how absolutely ethereal and gorgeous this cover is. I do judge books by their cover and this one is 5/5.

I really love the plot and set up of this book, it definitely led to the ethereal feeling. It’ll be interesting to see how this series continues!

This book is so beautifully written! I'm beyond excited to have got the opportunity to ready it, it was such a fun read.

A Letter to the Luminous Deep by Sylvie Cathrall. Obssesed - a new 5 star fantasy read. I am so excited to see where this series goes and how the author develops her craft! This uterly inventive scifi-fantasy novel is told episoltary style = bestill my heart. The story is told from two people trying to uncover why their siblings musyteriously disappared through books, jounals, letters and texts. This interesting structure was perfect for not only unraveling a mystery but also a beautiful love story, friendship and family. Scholar Henerey Clel has my heart <3

"P.S. I can’t believe E. started this whole thing by sending him a letter out of the blue. He loved that, I’m sure. He also loved her – even surer."

Cozy Fantasy • Mystery • Romance Subplot
Published 25 April 2024

Thank you @netgalley and @orbitbooks_us for the digital review copy 🪸🐚 🌊💘

The cover of this book is magnificent and absolutely drew me in, along with the synopsis which described this as a “whimsical epistolary fantasy set in a mystical underwater world with mystery and heart-warming romance.”

Unfortunately, I had issues with the writing style, the plot (circuitous, contrived, with logical issues), and the pacing. The main characters are 3 siblings and they're SOs, although they don’t trust each other/can’t get over their own selves enough to confide in one another until the final pages of the book. I put this book down for two months after reaching the mid-point with little plot revealed. The end of the book is a non-ending leaving the mystery unanswered, with it “to be continued” in the next book.

I credit the audiobook as a factor that allowed me to finish. The multi-cast narrators did a nice job bringing these characters to life. Some other positives: queer rep and disabilities rep both very normalized throughout the book.

"A Letter to the Luminous Deep" tells the story of two people trying to piece together the last days of each of their siblings, who disappeared while in each other's company, never to be seen again. The story is told through a series of letters between Sophy and Veyrin. But to piece together what happened to E. and Henerey, they share letters written between the pair that demonstrated their unfolding romantic attachment as well as research that they've done into the events mentioned in the letters and other secondary sources. There are also extensive explorations of mental health among the characters as well in an open and matter-of-fact manner, which is refreshing to see.

By using letters, each new revelation is relatively short and the book moves swiftly. However, there are a lot of characters, most of whom with unusual names, so it makes for a challenging read at first. Thankfully, once you get the swing of who's who, the story picks up pace and the various letters showcase an unusual world and culture unlike our own.

While it took a while for me to get into the book, and I had to pay close attention while reading it or risk having to re-read passages to figure things out, I did the enjoy the story and was eager to find out how it all turned out.

Imagine my surprise, though, when the story ended in a cliffhanger! There is nothing in the description or the book to indicate it's the start to a series or that another book is soon to follow. (Or even when a second book might be available.)

So as I'm writing this review, I'm feeling conflicted. Epistolary novels are always harder to read, so to make it to the end requires a keen desire to know how things will turn out. The relationships are predominantly with same-sex partners, which isn't "my thing." Add in the surprise cliffhanger, and I'm left feeling a bit disappointed.

However, the writing is strong, the story is compelling, and the worldbuilding is intriguing. And I still want to know how the story ends. Lol! And when a writer can take their reader to a place where they willing suspend disbelief, it's always a beautiful thing. So, whenever the mysterious Book 2 does come out, I'll be eager to read it.

Thank you to Sylvie Cathrall, Orbit Books, and NetGalley for an advance review copy.

A Letter to the Luminous Deep is such a unique story told in an epistolary format. I have tried to explain what this book is about, and though it is not hard to understand while reading, the world is crafted in such a way that pitching it is hard. The characters are so honest with each other and those around them in their mental health struggles while also facing a mysterious unknown. Even though you are only reading letters, these characters feel so real. The imagery of the underwater world is unmatched as well. Please give this one a shot.

Really different story style, both in the epistolary format but also the plot. It's quite a slow burn, but I continue to find myself intrigued enough to keep reading.

This had such promising elements to it but ultimately I had a really difficult time with the writing style of letters back and forth.

If epistolary novels are not your thing, then give this a pass. If slow-moving, old-timey prose in the style of the upper class in the19th century is not your thing, then give this a pass.

Otherwise, you are in for a treat in this absolutely wonderful story of four people getting to know one another, and a mystery of what caused the deaths of one of the pairs.

Author Sylvie Cathrall situates her story in a world a thousand years after a catastrophic event that dropped the book's population's ancestors onto an ocean planet. Earth is an ocean planet, too, but on the world in the novel, there is very little land, save for an atoll which houses a variety of campuses devoted to learning, some reefs, and floating habitations. A variety of technologies exist for traversing and living on the ocean's surfaces and depths, and at year after the story's opening, it appears that something like email has been created.

Years earlier, a genius architect constructed a home joined to a coral reef, and raised her three children there. Later, only E. Cisdnosin lives in the underwater home, while her younger sister Sophy is part of a research trip to a deep ocean trench with other Scholars*, while their artist older, irresponsible brother is off doing something elsewhere.

After E. sees strange behaviour from an unknown eel-like creature, she writes to Scholar Henery Clel, and gradually the two develop a relationship that starts as a discussion about underwater life, and gradually becomes a romance as they share their feelings, beliefs, and desires, something that is very hard for E. to do as she is a recluse in her home because of her “Brain” (she suffers from obsessive-compulsive disorder). E is a straightforward, thoughtful person, and she immediately engages the sensitive and kind Henery's interest with her questions and observations. There letters feel like something out of a Victorian novel, with their careful, formal phrasing that reads initially as extreme politeness, and sensitive consideration of each other's emotions.

E. also tells Henery of an odd structure that has appeared outside her home that causes her consternation but also ignites her curiosity.

A year later, Sophy begins a correspondence with Henery's elder brother Vyerin. Both are grieving, as E. and Henery are believed to have died in an explosion that destroyed the Cidnosin underwater home. They decide to share E.'s and Henery's letters with each other to determine what led to the explosion and their deaths, and also share their own histories and experiences with each other, such as Sophy's time as part of the research expedition and its unnerving results. And the two become fast friends. All this leads to a decision by Sophy and Vyerin that will play out in the next book.

I fell in love with this gorgeously written novel. I fell in love with E. and Henery and their tentative steps together, then I fell in love with their siblings Sophy and Vyerin.

I loved the tone of the letters, whether between E. and Henery, or Sophy and Vyerin. I adored the way the Cathrall took an unhurried approach to the unfolding of the respectful, gentle relationships, and to the revelations.

I loved this world of different scholar campuses, the persnickityness of the Scholars, the way Scholar Rawsel figured in Henery's and Sophy's past, and the questions raised as I read, such as
-what happened to drive these people's ancestors to the planet?
-what are the structures referenced in the subsequent histories?
-what really happened to E. and Henery?
-what is going on with Scholar Rawsel?

This book was a delight from opening page to its end, which left me very eager to continue “The Sunken Archive” series.

Thank you to Netgalley and to Orbit Books for this ARC in exchange for my review.


* Scholars can be scientists, medical professionals, artists, explorers, etc. after graduating.

This book is unique as I’ve never read a book quite like it.

Imagine finding a box of letters, and getting to go through them.. It would be easy to get swept away in the tales the letters provide of a different time. . Thats what this book feels like.

This book really goes into detail about sea creatures, academics, and the relationships in between.

While I thought this book was clever, it also had its down sides. I’m not going to lie…. I was bored.

Reading about sea creatures didn’t appeal to me, Also, the action is minimal.

Overall, a beautifully written book, that may cause drowsiness at times.

Thank you for netgalley and publishers for giving me the opportunity to read this book.