Exo with a coffee cup in a car

Review: Exo by Colin Brush

Posted on by Anna and Alexis

Alexis:

Exo comes out on November 18th, 2025!

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.

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! ⁣

VERDICT: ⭐⭐⭐.5 /5 

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Published by Anna and Alexis

Hello! We're Anna and Alexis, twins from the Richmond, Virginia area. We both studied English and creative writing in college. Anna spent a year after college working in book publishing in New York City. After living outside of D.C., she moved back to the Richmond area. She works in marketing. Her favorite genre to read is literary fiction, especially by female authors, and she also enjoys dystopian novels. Alexis works in marketing and writes novels on the side. She recently finished grad school, where she received her MFA in creative writing. She loves reading fantasy, especially YA, magical realism, and the occasional lyrical fiction and romance. We’ve been reading and writing together as long as we can remember, and we’re excited to share our bookish thoughts with you! Check us out on Instagram @takestwotobookreview.

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