Body Of Lies – Kat & Lock #4

Author: Jo Callaghan
Genre: Crime Thriller, Police Procedural
448 pages
Publisher: Simon & Schuster UK, 2026

Synopsis
Human suspicion. AI manipulation.
Who can you trust when truth has no meaning?

DCS Kat Frank returns to work at the Future Policing Unit after a tragic loss, only to find herself thrust into a new high-profile case. On the night of Halloween a local MP is found murdered, with a taunting message written in binary code that seems to target Kat Catch me if you can.

The victim’s anti-AI sentiments suggest a political motive, and as Kat investigates with her partner AIDE Lock – the world’s first AI detective – she finds herself once again battling her own prejudices about the technological future he represents. But when a cyberattack takes out the National Grid, Kat and Lock have to race against the clock to track down the hacker before thousands die.

Tangled in a web of suspicion and deception, Kat must choose who and what to believe when the truth seems to defy both instinct and logic.

Can she set aside her old doubts and put her faith in her AI partner one last time?
Or will this case send Lock down a path she just can’t follow – a path that will leave humanity behind for good?

My review
Body Of Lies by Jo Callaghan is the fourth and final installment in the exceptional Kat & Lock crime series, and it was easily one of my most anticipated reads of the year. Callaghan is a talented storyteller and her writing feels effortless. But what truly sets this series apart is its ambition. Beginning with In the Blink of an Eye, she has used the framework of a police procedural to explore artificial intelligence and, more importantly, what it means to be human. Across all four books, she raises thought-provoking questions about identity, consciousness, trust, and connection without ever losing sight of the story.

Callaghan also writes about grief and loss with remarkable honesty. Her characters carry their pain with them, but they also show resilience and hope in the face of uncertainty. It’s a difficult balance to strike, weaving emotional depth into a fast-paced thriller, and Callaghan manages it beautifully. That’s what makes this series stand out in a crowded crime fiction genre.

Body of Lies picks up a few months after the events of Human Remains. DCS Kat Frank has returned home and back to work, but it’s clear she’s still haunted by what happened and no longer fully trusts her own judgment. She continues to lead the Future Policing Unit, though the team is struggling after the loss of one of their own in the previous novel. Her AI partner Lock (AIDE: Artificial Intelligence Detecting Entity) is once again by her side through the wrist device Kat wears, but Lock’s growing desire for a physical human form leaves Kat uneasy. As much as she depends on him she’s still not able to fully trust him.

While this novel can certainly be enjoyed on its own, I strongly recommend starting with In the Blink of an Eye. The evolving relationship between Kat and Lock is the heart of the series, and watching that partnership grow and change over four books is what makes this series so unique.

There is so much packed into this final installment. The pacing is relentless, the mystery is compelling, and the themes feel especially relevant in a world where AI is becoming part of everyday life. What stayed with me most, though, was Callaghan’s portrayal of grief. She understands that loss doesn’t simply disappear. It lingers in quiet moments and shapes people in ways they often don’t recognize themselves.

Callahan clearly had a beginning, middle, and end planned for this series and she pulled it off brilliantly. The ending was emotionally resonant and true to the characters’ journeys. If you’re looking for a read that will challenge your mind, grip your heart, and keep you on the edge of your seat, the Kat & Lock series is it. I can’t wait to see where she takes us next!

My recommendation: absolutely worth the read!