If your kid just finished the first book in The Naturals series and is vibrating with excitement for the sequel, they’ve got good taste—and they’re about to get a much darker education in the second installment. Killer Instinct is effectively Criminal Minds for the YA set, and Jennifer Lynn Barnes doesn’t treat the "teen" label as a reason to pull her punches. It’s fast, it’s twisty, and yes, it’s significantly more intense than the first book.
TL;DR: Killer Instinct is a high-stakes psychological thriller that follows five teen "Naturals" as they hunt a copycat serial killer. It’s a masterclass in deductive reasoning and pacing, but parents should know it leans harder into crime scene descriptions and psychological trauma than its predecessor. If your teen loved A Good Girl's Guide to Murder or The Inheritance Games, this is their next obsession.
If the first book was the "onboarding" for how the FBI’s secret teen program works, Killer Instinct is the field test. The story follows Cassie (a natural profiler) and her roommates—Dean (profiler), Michael (emotion reader), Sloane (math/stats genius), and Lia (lie detector)—as they get pulled into an active case involving a copycat killer.
The brilliance of Jennifer Lynn Barnes is that she doesn't just write "smart kids." She writes kids whose brains are specialized tools. It makes the "mystery" part of the book feel like a puzzle the reader is solving alongside the characters. It’s not just about who did it; it’s about why they did it and the logic used to find them.
Let’s be straight: this is a book about serial killers. While it isn’t "slasher movie" graphic, it is "pre-credits scene of a police procedural" graphic.
In Killer Instinct, the killer is mimicking a famous (fictional) murderer known as the "Pyromaniac." This means there are descriptions of crime scenes involving fire, staged bodies, and specific "signatures" left by the killer. Barnes focuses more on the aftermath and the psychology of the violence rather than the act itself, but for a sensitive reader, the clinical way the characters discuss blood spatter or victimology might feel heavy.
The real "intensity" isn't the blood; it's the psychological pressure. The characters are being hunted, their past traumas (like the disappearance of Cassie's mother) are weaponized against them, and the "found family" dynamic is tested by secrets. It’s a lot of emotional weight for characters who are technically still supposed to be doing high school homework.
It wouldn’t be a Barnes book without a love triangle, and Killer Instinct leans into the Dean vs. Michael debate.
- Dean is the brooding, traumatized son of a serial killer (high stakes!).
- Michael is the charming, slightly chaotic "bad boy" with his own baggage.
The romance is definitely "PG-13." There’s plenty of pining, some intense staring, and a few kisses, but it never veers into "spicy" territory. The relationship drama actually serves a purpose—it highlights how these kids, despite being "Naturals" at reading everyone else, are still pretty bad at reading their own feelings.
Beyond the "can't put it down" factor, Killer Instinct is a workout for the brain. It encourages:
- Logical Deduction: The plot is a series of "if/then" statements. It rewards readers who pay attention to details.
- Media Literacy: It deconstructs the tropes of the "serial killer" genre. It’s a great jumping-off point to talk about why we’re obsessed with true crime.
- Complex Character Study: No one in this book is "all good" or "all bad." Even the "heroes" have manipulative streaks, which makes for much better conversation than a standard black-and-white morality tale.
If your kid is deep in the Naturals rabbit hole, don't just let them finish and toss the book aside. This series is a gateway to a dozen other interests.
- Talk about the "Naturals" skills: Ask them which "power" they’d want. Would they rather be able to tell when anyone is lying (Lia) or be able to see patterns in numbers (Sloane)? It’s a fun way to talk about their own natural strengths.
- The "Criminal Minds" Connection: If they’re 14+ and handle the books well, they might be ready for actual procedurals. Just be prepared for the jump from "reading about it" to "seeing it on screen."
- The "Why" Question: Ask them: "What makes a person a 'Natural' vs. just someone who practices a lot?" It’s a subtle way to talk about talent vs. hard work.
The biggest friction point in Killer Instinct isn't the "bad stuff"—it's the cliffhangers. If you buy book two, go ahead and have book three, All In, ready to go. The series is designed to be binged.
Also, the "parental figures" in this book are... complicated. The FBI handlers are often keeping secrets or using the kids as bait. It’s a classic YA trope (adults are incompetent or untrustworthy), but it’s worth noting if your kid usually prefers stories where the "grown-ups" have everything under control.
Q: Is Killer Instinct appropriate for a 12-year-old? It depends on the 12-year-old. If they’ve read The Naturals and weren't bothered by the crime elements, they'll be fine. If they are sensitive to themes of child endangerment or detailed crime scenes, you might want to wait a year.
Q: Do you need to read book one first? Absolutely. This isn't a "monster of the week" series where you can jump in anywhere. The character arcs and the overarching mystery of Cassie’s mother rely entirely on the events of the first book.
Q: Is there any "spice" or inappropriate content? In terms of romance, it’s very tame—think CW-level teen drama. The "inappropriate" content is almost entirely focused on the violent nature of the crimes being investigated.
Q: How does it compare to The Inheritance Games? The Inheritance Games is more about riddles and "low-stakes" family secrets. The Naturals is much darker, dealing with actual FBI cases and life-or-death situations. If they liked the Inheritance puzzles, they'll like this, but they should be prepared for a mood shift.
Killer Instinct is a high-quality thriller that treats its audience like they’re smart enough to keep up. It’s intense, yes, but it’s the kind of intensity that builds critical thinking and engagement rather than just cheap shocks.
- For more high-stakes teen mysteries, check out our best books for kids list.
- If they want to move from books to the screen, see our best shows for middle schoolers.
- Explore more from Jennifer Lynn Barnes with our guide to The Inheritance Games.
