The Terrarium by Katie Collom: True crime, questionable women, and a cat-sitting job gone wrong

Annie has built a life around watching other people’s cats while they go off to enjoy the lives she wishes she had, but her latest cat-sitting assignment offers more excitement than she bargained for in The Terrarium by Katie Collom. When a mysterious client leaves Annie in charge of her cat, Hades, without ever meeting her in person, Annie begins to suspect that the glamorous house holds secrets far more sinister than an eccentric homeowner’s locked doors.

For a true-crime enthusiast who spends her free time speculating about murder cases, the possibility that her client might be a serial killer is an irresistible mystery. This darkly humorous suspense novel delivers an entertaining cast of women whose behavior ranges from questionable to downright alarming, even if a few structural choices kept me from enjoying the story as much as I might have.

Annie is an entertainingly unreliable guide to the events unfolding around her. She knows enough about true crime to recognize suspicious behavior, but her own judgment is hardly beyond reproach. Her life has stalled out, and she spends much of her time watching other people enjoy the opportunities she feels she has missed. The Cuppa Crime podcast and its online community give her a sense of belonging, allowing her to immerse herself in murder investigations without having to do much with her own life. When Zoe hires her to care for Hades, Annie gets a glimpse of a lifestyle that seems far more glamorous than her own. The fact that Zoe refuses to meet her in person only adds to the appeal of the mystery.

Of course, Annie’s curiosity is not the only questionable aspect of her character. She has a habit of taking souvenirs from her cat-sitting assignments, which makes her a less-than-innocent observer of other people’s lives. Her encounters with Zoe’s neighbor and former clients add another layer of absurdity to her already complicated circumstances. Deborah, who believes Annie killed her elderly cat, seems determined to keep tabs on her, while Zoe’s neighbor takes an almost suspicious interest in Annie’s activities at the house. One might think that a woman looking after a cat would be allowed to get on with the job, but Annie has a knack for attracting people who seem to have decided she is up to no good. The irony is that, given some of her habits, they are not entirely wrong to be suspicious.

The novel is chock-full of unstable women, and Collom has fun playing with the gap between how these characters see themselves and how they appear to everyone else. Annie’s enthusiasm for true crime encourages her to interpret the peculiar details of Zoe’s house as potential evidence of something terrible. When objects connected to ongoing murder investigations begin to appear among Zoe’s belongings, Annie must consider whether she has stumbled onto an actual crime or simply become too invested in her own theories.

The house itself provides an effective setting for this uncertainty, especially with a room Annie is expressly forbidden to enter. Zoe’s absence gives Annie plenty of space to imagine what might be happening behind the scenes, and the humor comes in part from watching her try to make sense of a situation in which she is hardly a neutral observer.

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I enjoyed the book’s willingness to let Annie be a messy, sometimes ridiculous protagonist rather than a conventional amateur detective. Her questionable decisions create complications that a more sensible character might have avoided, and her tendency to turn ordinary encounters into potential criminal investigations makes for some amusing moments. The suspense works best when Annie’s imagination and the evidence in front of her seem equally capable of leading her astray. I had fun following her attempts to figure out what Zoe might be hiding, even as I occasionally wanted to tell Annie to stop making things harder for herself.

One structural choice, however, repeatedly interrupted my enjoyment. Two true-crime podcasters provide commentary on the events, sometimes in their own separate vignettes and sometimes by dropping a line or two directly into the middle of the action. I had no real problem with the standalone sections devoted to the podcast. They fit the novel’s interest in true-crime fandom and offered another perspective on the story. The interruptions within scenes were a different matter. Rather than adding useful context, these asides often pulled me away from what Annie was experiencing at the moment, making it harder to remain immersed in the suspense.

The more significant problem was the disconnect between what the podcasters appeared to know during these interruptions and what they knew when they eventually interviewed Annie on their show. Throughout the novel, their commentary suggests that they have access to everything Annie knows and does as the story unfolds. By the time they speak with her directly, however, their understanding seems limited to what Annie admits to having done. Those are two very different versions of events. If the podcasters have been commenting on the full story in real time, their later interview should reflect a different level of knowledge than it does. I found myself wondering how these sections were supposed to fit together, and the inconsistency weakened a narrative device that might otherwise have been a clever extension of the book’s true-crime themes.

I also found myself wishing the ending had taken a slightly different direction. Without spoiling the outcome, I will say that anyone familiar with my fondness for books about women who deliver justice to bad men can probably guess what I was hoping for. I wanted a resolution that leaned a little further into that impulse, and the conclusion did not quite give me the satisfaction I wanted. That does not erase the fun I had with the novel, but it did leave me wishing Collom had made a different choice about where Annie’s story would ultimately lead.

The Terrarium is an entertaining pick for readers who enjoy dark humor, suspicious neighbors, amateur sleuths with questionable ethics, and mysteries populated by women who are not always easy to like. Annie’s misadventures kept me engaged, and the novel’s blend of true-crime obsession and domestic suspense gives it plenty of personality. The interruptions from the podcasters and the disconnect in their knowledge held the story back for me, while the ending left me wanting a different kind of justice. Still, I had a good time with this one, and readers who enjoy their suspense with a generous helping of absurdity may find that Annie’s latest cat-sitting job is worth investigating. The Terrarium by Katie Collom will be published on November 10, 2026.

Do you enjoy unreliable narrators who make questionable decisions, or do you find yourself wanting to shake some sense into them? And when a mystery involves a character who may be guilty of something herself, do you root for her to get away with it or hope she finally faces the consequences? Let me know what you think in the comments!

An advance reader copy of this book (ARC) was provided to me by the publisher via Netgalley in exchange for an honest review.

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