Jump to ratings and reviews
Rate this book

Exo: A Novel

Rate this book
A debut sci-fi mystery set on an abandoned future Earth, featuring a twisty mystery straight out of a John le Carré novel, a group of larger-than-life characters who’d be at home in the work of John Scalzi, and a deeply weird and dangerous hyperdimensional entity to haunt the dreams of any reader of Kim Stanley Robinson.

Humanity is dying. Banished from the Earth, our descendants eke out lives in orbital habitats and moon colonies––and look with longing on our former home.

But Earth is uninhabitable. Over hundreds of years, its oceans have transformed into an annihilating liquid entity––the Caul. Every living creature approaching its shores is irresistibly compelled to enter. . . and is never seen again.

Scientists working in facilities seek to understand and stop the Caul. And scavenging the shores are the penitents––those who resist its siren lure.

Penitent Mae Jameson, an octogenarian former Service agent who arrived on Earth thirty years ago to find her lover, encounters Siofra, a mute girl, wandering alone by the shore. Back at Siofra's camp, Mae finds the girl’s father, rogue scientist Carl Magellan, hanging from a noose. He's been murdered. Unwilling to leave it in the hands of the facility Carl abandoned years ago, Mae takes Carl’s journals and sets about investigating.

The journal details Carl and his deceased wife's obsession with the Caul and its mysteries, even as it takes a debilitating toll on them.

In this page-turning, dual-timeline novel, both Mae and Carl's quests for the truth put them at the center of a dangerous conspiracy. Someone believes they can use the secret of the Caul to shape humanity's future, and they aren't afraid to kill to keep control of it.

354 pages, Kindle Edition

Published November 18, 2025

7 people are currently reading
1095 people want to read

About the author

Colin Brush

2 books10 followers
Colin Brush was born in Scotland and raised on the Channel Island of Jersey. After studying geology in Glasgow, he moved to London and started working in the book trade. Over the last quarter century, he has written the cover copy for over 5,000 books. He lives with his partner and their daughters on the southeast coast of England, a few miles from Dungeness, the sea-shaken wilderness that is the inspiration for his first novel Exo. He posts about writing and copy as colinthecopywriter at his website, on Bluesky and Instagram.

Ratings & Reviews

What do you think?
Rate this book

Friends & Following

Create a free account to discover what your friends think of this book!

Community Reviews

5 stars
6 (13%)
4 stars
18 (40%)
3 stars
13 (29%)
2 stars
6 (13%)
1 star
1 (2%)
Displaying 1 - 26 of 26 reviews
Profile Image for Faith.
2,234 reviews678 followers
November 19, 2025
The story is told in two timelines that converge. Earth has become almost uninhabitable, and life there is dominated by the Caul which has taken over most oceans and lures people to their death. In the recent past, Carl Maxwell and his wife have come to Earth to research the Caul. After his wife dies, Carl is left alone with their young, mute daughter Siofra. In the present, Mae is a former investigator, who came to Earth decades ago in search of her husband. She leads a solitary life until Siofra approaches her with a cryptic note. When returning Siofra to her home, Mae discovers that Carl has been murdered. Mae attempts to find the murderer, while protecting Siofra.

If the phrase “hyperdimensional entity” means something to you, then you will probably understand this book better than I did. I was completely confused by the Caul. However, I did enjoy the writing style and the narration of the audiobook. I actually liked both timelines and the way in which the they converged. That is unusual for me. I was intrigued by the mystery surrounding Siofra. Other than the descriptions of the Caul, I didn’t get any feel for how people were actually living on Earth. There was no mention of commerce, other than the occasional barter. They were trapping animals for food, yet they had vehicles and fuel and vodka. There were doctors, but where did they get medicine? Basically, I did not think that the world was very well fleshed out. 3.5 stars

I received a free copy of this audiobook from the publisher.
Profile Image for domsbookden.
217 reviews12 followers
November 15, 2025
*2.5

Sci-fi mystery is quickly becoming a favorite genre blend of mine, but Exo didn’t deliver on the aspects of the genre I enjoy most. The pacing is sluggish and lacks momentum, with the story unfolding too slowly to sustain engagement. What should build tension instead dissipates it, and the narrative never quite generates the propulsion it seems to promise.

The world-building gestures toward complexity but stops short of realizing it in any concrete or immersive way. The setting feels more conceptual than tangible—an idea of a world rather than a lived one. Environmental and social details are too sparse to ground the story in any real sense of place. The world operates largely at a theoretical level, with little material or sensory anchoring, which makes it feel hollow despite its intellectual ambition.

The prose was competent but lacked vitality. The diction was precise and controlled, but it didn't evoke much atmosphere or texture. The writing functions well on a technical level but lacks energy, resulting in a style that felt measured to the point of dryness. The characters and their interactions with each other were emotionally distant, making their motivations feel obscure and inconsequential. It was very hard to connect with anyone when the story itself felt detached.

Overall, Exo proves interesting in concept but not in experience. It aims high intellectually, but without the emotional depth or sensory richness needed to bring its ideas to life, it falls short of fulfillment.

Thank you to NetGalley and the publisher for this ARC in exchange for an honest review.
Profile Image for Maria.
229 reviews
November 7, 2025
The Caul (short for Cauldron) has taken over Earth's oceans. Most humans reside off-planet, after a mass exodus when the Caul appeared. Some people are "called" to return to Earth by the Caul, and some scientists have been dispatched by a clan to study it and figure out what it actually is. Anyone who enters the Caul disappears. Some people believe it is some sort of religious thing, some an alien thing, but no one really knows.

The story has 3 main parts - what is currently going on with Mae (a "penitent" who lives alone and scavenges out a living on the mostly abandoned Earth) and Siofra (the Magellans' mute daughter), what happened over the past 9 years with Carl and Gemma Magellan (the scientists) leading up to the start of Mae and Siofra's story (told from the perspective of Carl's journals), and Mae's past (told sort of in flashbacks, but less flashback-y and more narrative).

Mae is technically a member of one of the religious groups (the penitents) but really she came to find her husband, who left Mars suddenly out of seemingly no where to go to the Caul. She lives on her own, bartering with several other individuals also living in the wilds to eke out a meager living. The Magellans (Carl and Gemma) were scientists at "the facility" but they struck out on their own when the higher ups of their expedition prevented them from going near enough to the Caul (and the topology near it) to study it the way they wanted to. Their daughter, Siofra, is around 6 or 7, and has never spoken. When Mae finds Carl dead, and determines it had to have been murder, she takes Siofra in (Gemma disappeared years ago, presumably into the Caul) and begins investigating what happened to Carl.

The 3 storylines were very good, and intertwined interestingly. The characters were unique, though some were not fully developed. The mysteries (who killed Carl and what the Caul actually is) are interesting. The science (mostly focusing on the mathematical branch called topology) was interesting, but a bit over my head. What I know about topology I learned from Dennis E. Taylor's Bobiverse books and the megastructures encountered therein. It was enough to get me through with a general idea of what Carl and Gemma were studying. I enjoyed the story, and would recommend it for sci-fi mystery fans.

The audio narration was good, but sometimes the pacing of the narration felt significantly slower than the pacing of the narrative. Particularly at the very beginning of the book, where I felt that the narrator was reading deliberately slowly to increase the drama, but it just made me tune out and have to relisten to the first few chapters. Also some of the characters (all voiced by a single narrator) seemed to ALWAYS be yelling. Meaning I was constantly adjusting the volume to turn down the strident, yelling voices (like Dr. Carlisle), and quickly turn back up for the quieter voices (like Mae).

I received an ARC of the audiobook from #NetGalley.
Profile Image for Brandon B.
16 reviews3 followers
November 29, 2025
Exo by Colin Brush is a gripping sci-fi debut that pulls you into a desolate future Earth where humanity’s remnants orbit above, leaving the planet to its own eerie devices. The story follows an aging agent unraveling a scientist’s murder amid the mysteries of the Caul, this weird, deadly ocean-like entity that’s both terrifying and fascinating. Brush weaves in spy thriller vibes reminiscent of le Carré with some mind-bending multidimensional elements, keeping the plot twisting without getting too bogged down in jargon. It’s got flawed characters you can root for, like the enigmatic mute girl who adds a touch of humanity to the chaos, and while the dual timelines took a bit to click for me, once they did, I couldn’t put it down. Overall, a solid read for anyone into post-apocalyptic puzzles with a cosmic edge, definitely worth checking out if you’re craving something fresh in the genre.
Profile Image for Katie.
512 reviews
November 26, 2025
Thank you NetGalley and Dreamscape Media for the ARC of this audiobook.

I was not a fan of how the narration was done. It was supposed to be two different characters, a male and female, and after some time, it got confusing on who was supposed to be talking and where you were supposed to be in the book because of the narratos voice. I think if you are going to have a dystopian book with some world building, it would be recommended to have different narrators for the audiobooks to make the listening experience so much easier.

I really liked the idea of the plot, but it fell through the cracks, and I can't figure out why. I just felt really bored by it all and I typically love dystopian stories.
Profile Image for Rupert Nacoste.
Author 5 books16 followers
December 26, 2025
When I finished this novel, I said to myself, that's a really nice piece of science fiction. Examples, for me, of "a really nice piece of science fiction" include the Tom Cruise movie "Oblivion." Nothing spectacular, but an engaging story from beginning to end.

Exo, also put me in mind of Ben Winter's "The Last Policeman." In that one, we know the world is coming to an end because a giant comet is on the way, and unavoidable. But someone is murdered, and a policeman cannot stop himself from trying to solve the murder even though...yeah, the world is coming to an end.

In Exo, we humans can no longer live on Earth. Earth has been decimated by our carelessness. Not only that, the climate of Earth has now been taken over by some creeping, crawling, oozing, climate stuff that seems made up of structures that may be multidimensional.

Even so, some humans have left the other planets and asteroids that humanity has escaped too, and come back to Earth for a variety of reasons; scientific and religious. These motivations are not of one type, but many types of say "religions." And then there are the penitents who find ways to live on Earth, as they do penance for our past climate transgressions.

Earth really is unlivable. And then someone is murdered and one of the penitents, Mae Jameson, an 80 year old former "policeman" decides she has to figure out who did the murder. But why? I mean there are no courts, no prisons, that the hellish landscape that is earth.

Well there is that and a child. A child that is at the heart of what turns out to be a scientific and religious mystery. We go on a journey of discovery with Mae, and it is well worth the trip.

This is "a really nice piece of science fiction."
Profile Image for Elisa.
4,291 reviews44 followers
November 5, 2025
Humans haven’t fared too well in the future and survivors live on colonies across the solar system, Earth is deadly due to “the Caul,” some kind of fog-type possibly sentient entity. It drives people crazy and suicidal. A couple of scientists move back from the colonies to study it. This story is told by diary entries read by a woman in their future. She is taking care of a small girl whose father died by suicide. As is obvious from my feeble attempt at a recap, the plot is complex and hard to summarize. It’s set in different timelines and they complement each other, but it’s not always obvious how. The characters are as foreign to us now, as people in the Middle Ages. Humankind has reverted to pure survival mode so, as easy as it was to understand how they might commit atrocities without real malice, it was hard to root for them. Gildart Jackson narrates the audiobook effectively, doing what he can to humanize these characters. I liked the world-building, bleak as Earth is, you can almost see the future of the planet. The murder mystery within the “present” was intriguing enough for me to keep trying to figure out whodunit. All that said, this is a good novel that I didn’t completely enjoy because it was a bit confusing. I might have had an easier time with the printed version than the audiobook. I’m also not a big sci-fi fan. It is well written and proposes interesting ideas so, overall, it’s worth reading.
I chose to listen to this audiobook and all opinions in this review are my own and completely unbiased. Thank you, NetGalley/Dreamscape Media.
Profile Image for Sofia.
857 reviews22 followers
November 11, 2025
I will be honest, I did like the story, but the narration wasn’t on point, let me explain why. For me this book was like a tree with two branches. In one of the branches, the main point of view is from one couple of scientists and in the other an old woman, but she doesn’t feel old, is weird…
The narrator was always the same and the two branches were read by the same person, pretty much in the same manner, and I missed having a female voice there, sometimes that is not the straw that break the camel back, but for me in this book it was, because it felt more slow and dragging the story, and every time the point of view changed I would lose my ground and take a while before realizing who was speaking now, but to be fair, let me just say it out there, English is not my first language and perhaps the problem is in my end (of getting lost) and not from the narrator.

Would I try to get a written copy? Most definitely yes, I did like the story, I know both stories are meant to converge, because in the end the past talks about a character that isn't in the present in the book, so it would be more worthwhile for me if we had at least two voices, and some books are more appreciated in the written form, and I think for me this is one of these few books.

Thank you Netgalley and Dreamscape Media, for the free AAC and this is my honest opinion.
Profile Image for Alexis Collins.
102 reviews11 followers
November 8, 2025
3.5 stars rounded up

In Exo, Brush explores a myriad of classic sci-fi themes, including environmentalism and what it means to be human.

The Caul itself was almost impossible to picture, yet Brush’s descriptions mirror the alien vastness of the invading substance. I’ve read sci-fi books with post-apocalyptic Earths before, but the Caul was a very unique and fascinating entity.

The story goes back and forth in timelines. In the present timeline, Mae, an old woman and ex-policewoman, finds rogue scientist Carl dead—murdered—and his daughter, Sofria, on her own. In the past timeline, we’re reading Carl’s scientific and personal diary entries about his arrival on Earth and study of the Caul.

I did enjoy this book as a whole; however, it’s not really a twisty murder mystery. Exo is a scientific, mathematical kind of sci-fi book. While it is gritty, it’s a haunting, slow moving book that you have to read slowly to ponder over. The murder mystery and investigation take a backseat to the Caul and Mae trying to help Sofria, and nothing really gets solved until the very end of the book. Yet I enjoyed learning about the Caul, Mae and Sofria, and Brush’s prose, and the ending was satisfying!

Thanks so much to Diversion Books for my ARC in exchange for a review! ⁣
Profile Image for Silvia  RoMa.
1,037 reviews7 followers
November 10, 2025
*2.5 stars

I love dystopian novels and I love thrillers, so I thought this one was going to be a new favorite for me. However, it didn’t deliver on the aspects of the genre I enjoy most.

The pacing is super slow and lacks momentum, with the story unfolding too slowly to keep the reader entertain and engaged throughout the book. What should build tension instead dissipates it, and the narrative never quite generates the propulsion it seems to promise.

The world-building gives the impression of complexity but it's lacking. The setting is interesting and it's one of the things I liked more about the novel.

The prose was alright but I did not enjoy the audiobook narrator, it felt too monotone for my taste and that made the book feel even more slowly.

I didn't care much about the characters because It was very hard to connect with anyone as they felt quite distant and disconnected from the story.

Overall, the novel was alright. The setting and premise are interesting but at the same time too slow to grad the readers attention till almost the very end.

Thank you to NetGalley and Dreamscape Media for an ALC of this novel, all opinions are my own.
Profile Image for Esme.
990 reviews50 followers
December 8, 2025
A very solid Sci-fi dystopian. I enjoyed my time reading it. I think the book lacked a bit in the world building. I think I had a bit of an advantage since the book reminded me of the video game 'Death Stranding' so I projected a lot of that world building onto this book which helped me visualize everything better. When building a world like this I always wish the book was longer, I just don't feel like we had enough time to really fully paint the full picture.

The characters I enjoyed. I felt like everyone was written well and served the story. We had a few different story lines and the characters were all easy to tell apart, I was never confused on which POV we were following.

I'm not going to pretend I understood any of the scientific/mathematical terms but honestly it didn't affect me understanding the story which I appreciated.

The narrator did a good job, but this is a book that would benefit with multiple narrators for each POV's to really elevate the experience.

Overall it's a good Sci-Fi. I 100% recommend it if you've played 'Death Stranding' and wanted a similar world to immerse yourself in!
Profile Image for Country Mama.
1,432 reviews65 followers
November 7, 2025
Exo by Colin Brush is a debut sci-fi thriller by the author about human beings living out in orbital habitats with an abandoned earth. Earth is abandoned by people due to a climate disaster, which makes the planet unlivable for us humans, along with an ocean that is trying to consume everyone in it's path., aka known as The Caul. The characters of Mae and Carl are well written and relatable to the readers. I really liked the dialogue between the characters and the story itself was super interesting to me as a reader. I enjoyed how the author made up a whole world in the habitats and how humans would exist outside of our planet, inside stations or habitats. I thought Mae's ending is fitting for the book and also leaves the story open for another book or more to the story. I think that the author did well on his debut into the world along with the dual time line part of the story, which works well for this one. I recommend to fans of sci-fi reads and dystopian/another world or time line reads!
Profile Image for Cindy.
1,731 reviews37 followers
November 8, 2025
Terrific hard sci-fi debut that takes place mostly back on Earth long after humans fled the collapsing planet for Mars and orbital stations. A few scientists have returned to study the Caul, an impenetrable and indecipherable miasma of a substance that "disappears" those who enter it. Carl Magellan keeps diaries but, when he is found dead, one of his journals is missing. Who killed him and why? We learn about the world through his diaries as well as through Mae, who decides to investigate Magellan's death if only to find answers for herself and for his daughter. There's a real sense of place and a noir mood to this mystery novel. The story itself is complex, and Earth is definitely a character/presence to be reckoned with. The audiobook narration is very good, with emotion and even strident yelling in places (as appropriate).
My thanks to the author, publisher, @DreamscapeMedia, and #NetGalley for early access to the audiobook of #Exo for review purposes. Publication date: 18 November 2025.
Profile Image for Emily.
155 reviews2 followers
November 17, 2025
I made through 50% of the audiobook before deciding to DNF. There’s definitely a strong foundation here—some solid world-building and a sense of intrigue that I think will appeal to certain readers. Unfortunately, the pacing felt too slow for me, and I struggled to stay engaged as the plot dragged.

I also found that there were quite a lot of characters introduced early on, but not enough development for me to really understand who they were or how they fit into the larger story. That made it difficult to stay grounded in the narrative.

The audiobook narrator was fine. Their delivery felt a bit slow for my preferences, even with adjustments to playback speed.

Overall, while this one didn’t work for me personally, I can see it landing well with readers who enjoy sci-fi mystery, slower pacing, and a broad ensemble cast. Thank you to Colin Brush, Dreamscape Media, and NetGalley for the ARC!
Profile Image for Holly Taggart.
488 reviews8 followers
August 2, 2025
This is a gritty sci-fi otherworldly novel that I really, just could not get into! It might be for others, but it wasn't really for me.
It has many many features that I found interesting, a climate-fiction disaster in which Earth is no longer really livable and a transformed ocean which seems to be calling to consume everyone. The characters seem compelling, a mute child and an octogenarian who team up in an unexpected way... but yet the pacing just did not do it for me. The Atmospheric writing was bang on and I began to feel both dread and slight depression every time I started to pick up the story.
So this may be a book for other Sci -Fi lovers, as it definitely captured me into the atmosphere, but then I kinda of had to escape before I felt pulled under into the caul.
Many thanks to Net Galley and Diversion Books for the Advanced copy.
Profile Image for Jessica McCann.
249 reviews1 follower
November 15, 2025
Exo is a unique dystopia set on an ecologically compromised future Earth, where an ominous gray mass pulls living beings into it. The setting feels stark and real, lending ecological dread a sharp edge. The pacing can sag at times, and the protagonist makes a few credibility-straining choices, especially after a recent attempt to betray them. Yet the present-day murder mystery sticks with a steady rhythm that keeps you turning pages. The world-building is memorable and bleak, painting a future that lingers in the mind, and the ideas it raises are thoughtful and provocative. It’s well written, ambitious, and worth a read for anyone who enjoys big questions and a hard-edged atmosphere, even if a few sections demand patience.

Thank you to the publisher and NetGalley for an arc of this book. #NetGalley #arcreview #Exo 3 ⭐️story | 3 ⭐️ narration
Profile Image for Alice Liu.
Author 6 books20 followers
November 19, 2025
Exo's ending was beautiful...subtly pulling the threads together. However, I almost didn't get there. The alternating journal entries are bogged down with clinical, mechanical descriptions that do not serve the mystery. Instead of ramping up suspense, they just kept it flat, forcing the reader to experience the same monotony as the journal's writer. The character of Mae is so emotionally detached, that I thought she might have been autistic until an autistic character was introduced. Throughout, the reader is left to infer the emotions which would have been fine if the book had more heart and a little less mind. 4 stars for the ending but 3 stars for the rest of the book.
Profile Image for Dani.
239 reviews23 followers
November 13, 2025
Thank you to NetGalley for the ARC of this audiobook.

This was an intriguing listen, part sci fi thriller, part mystery. Mae Jameson is a strong lead, her investigation into a strange murder and a rogue scientist kept me turning the pages.

The narration added real depth, capturing Mae’s determination and the story’s tone perfectly. The shifts between timelines and perspectives were handled really well, making it easy to follow even as the story became increasingly layered.

A really impressive debut that blends sharp writing, strong characters and an original concept.
87 reviews10 followers
July 17, 2025
One of the best end of the world books I've read. It's two books - there's a mathy sci-fi story told in diary form then a parallel murder-mystery. This is a novel that challenges what grief means and what right we have to the planet. How do you deal with an existential threat that has no obvious intelligence or solution. How do you communicate with this threat? Should you?

This book is The Gone World meets The Drowned World in the best way.
Profile Image for J.
321 reviews2 followers
November 4, 2025
I received this DRC from NetGalley.

I just had a hard time getting into this one. The pacing was slow and on top of that, the main character was making decisions that didn't make sense. Why would you trust someone who had just tried to rob and strand you the day before? I think the setting was interesting, but the characters and mystery of it all just fell flat for me.
Author 2 books9 followers
November 26, 2025
NetGalley ARC

The actual writing is quite good and has impressive rigor and depth. also found many of the concepts quite interesting. however something felt off about how an autistic character was depicted, it just rubbed me the wrong way at times, and the jumping around between narratives was occasionally difficult to keep up with.
Profile Image for Dale Dewitt.
192 reviews5 followers
December 25, 2025
A wonderful mystery/detective story on a dying earth. It was a story that is Andy Weir and Agatha Christie had written a book together. Mae is a great character and I was engaged throughout the book. The visuals of the planet and topology was well crafted and took me to our dying planet in the 3000’s. Highly recommend!

I received an ARC from NetGalley for my honest review
3,601 reviews16 followers
November 4, 2025
lyrical and interesting sci-fi story with some unique ideas. would definitely recommend this one, because the world building is especially fantastic. 5 stars. tysm for the arc.
Profile Image for Becky.
245 reviews1 follower
November 11, 2025
Favorite quote:
"Any rights we have depend on others upholding those rights."
-May …
Displaying 1 - 26 of 26 reviews

Can't find what you're looking for?

Get help and learn more about the design.