I received an advance reader’s copy (ARC) of A Letter to the Luminous Deep by Sylvie Cathrall. Since this version is just a proof and not the final version, I won’t quote directly and will keep my comments general.

In A Letter to the Luminous Deep, E. Cidnosin lives in the Deep House, a technological marvel of an underwater dwelling. She is rather solitary, with her parents gone and both her siblings off living their own lives. But one day, she observes some unknown sea creatures out her window and takes a chance by writing to Henerey Clel, a renowned scholar, to ask his opinion. So begins a correspondence between the two of them, resulting in their falling in love—and their disappearance when the Deep House is mysteriously destroyed. A year later, E.’s sister Sophy and Henerey’s brother Vyerin begin exchanging their own letters in order to piece together what happened to their siblings. The more they investigate, though, the more they speculate that the world is full of more magic and wonder than they realized. And perhaps what happened to E. and Henerey is not scientific, but fantastical.

This is quite an impressive debut! The water-logged world we find ourselves in is quite rich in detail, with different societies (some on small islands, some nomadic on the waves, etc.) and different customs. It’s a clever setting, and I liked learning about it. The Deep House especially is a cool place, as one might imagine.

I also can’t recall ever reading a novel that’s entirely told in letters and documents. I’m sure they exist, I just haven’t encountered them. The closest thing I can think of reading (at least lately) is Divine Rivals, but that has plenty of regular prose. So this was a fascinating experience, challenging but rewarding. One has to exercise their skills at inferring and critical thinking even more than usual, gleaning through characters’ letters the nuances of their societies and actions. So cool.

Furthermore, the characters themselves are excellently written. E. is sweet but full of anxieties and low self-esteem, struggling to see her own worth while also being intelligent and charming. And Henerey is a delight, a total nerd with a romantic streak. Watching them fall for each other without even meeting in person was lovely.

However, my favorite dynamic was actually Sophy and Vyerin. The progression of their friendship was just wonderful. Yes, they only got to know each other because of the tragic loss of their siblings, but their relationship was also so genuine and based on mutual interest and respect, and I loved every second. In a way, they fell in love too, in a platonic sense. I loved seeing this example of how loss can bring people together, and how family can be chosen.

As for the plot, it’s a rather slow-paced one. There’s a lot going on, from E. and Henerey’s love story to Sophy’s investigations in the abyss and her own romance with her fellow researcher, from Henerey’s journeys on a ship to the strange object found outside of Deep House and what it means. (Sorry, I’m being vague to avoid spoilers.) Because of all this, we shift back and forth from plot thread to plot thread, but not at breakneck speed. It’s more about the research, and the connections between people, than action and excitement. That said, there are also some thrilling scenes, like Sophy’s encounter with a giant nautilus and another rather more spoilery sequence. And the final act certainly held some surprises, in terms of action and major events.

I must admit, I’m a little torn about how this book ended. I’d had it in my head that the explanation for E. and Henerey’s disappearance would be grounded in the reality of this watery setting as I’d come to understand it, rather than what actually happened. But I suppose that’s the point, that the world the characters knew would be challenged with new revelations. I just think the revelation that E. and Sophy’s mother had something to do with it felt a little less well-incorporated than it could have been. I don’t know, maybe I just missed the foreshadowing.

Either way, in the end, A Letter to the Luminous Deep was enjoyable. Cathrall proves herself adept at spinning an engaging narrative, rife with excellent characters and a cool setting. The epistolary, academic nature of the story made this a singular reading experience for me, even if I struggled a little with the ending. (And I wish I’d known this was the first book of a duology when I started, but hey, at least it’s not a trilogy.) I definitely think this is worth reading, and I’ll be looking out for more from this author in the future!