Body of Lies (Kat And Lock Book Four) by Jo Callaghan.
Published 21st May 2026 by Simon and Schuster.
From the cover of the book:
Human suspicion. AI manipulation.
When truth can be rewritten, who can you trust?
DCS Kat Frank is back at the Future Policing Unit after a devastating loss - and straight into her most disturbing case yet.
On Halloween night, a local MP is found murdered. Beside the body is a taunting message in binary code, aimed directly at Kat:
Catch me if you can.
The victim was a vocal opponent of AI. The motive looks political. But as Kat investigates with her partner, AIDE Lock - the world’s first AI detective - the case spirals into something far more dangerous.
Then a cyberattack takes down the National Grid.
With the country in chaos and lives on the line, Kat and Lock must track a killer who is always one step ahead. But in a world of deepfakes, deception and digital ghosts, instinct is no longer enough.
Kat must decide whether to trust the one thing she still fears most: her AI partner.
Because this time, Lock may not just be solving the case.
He may be changing what it means to be human.
Can Kat stop a killer before the lights go out for good?
DCS Kat Frank has not been home since the terrifying hostage situation that saw DI Rayan Hassan become collateral damage in a last ditch attempt to save her. Being back in the house means coming to terms with more loss and trauma - and deciding whether she can still trust her AI partner AIDE Lock.
She and her FPU (Future Police Unit) team need to pick themselves up and get back to work without Hassan, and the opportunity presents itself when an anti-AI campaigning MP is murdered and strung up for all to see on a historic pillory in Coleshill.
There is something strange about this case from the start. The local powercut that coincided with the murder is odd, and the killer seems determined to taunt Kat and Lock. But the full scale of the dark motivation behind the crime only comes to light when a massive cyber attack on the National Grid brings the country to a dangerous standstill - just as the government are considering an AI bill which might see Lock finally get the body he desires...
This concluding volume of the gripping Kat and Lock series is the most ambitious, tense, and thought-provoking of them all. When a slow-burn murder investigation blows wide open into a national security situation of epic proportions, Kat and her team must race against the clock to find a killer and a cyber-terrorist. With the country on its knees, and lives in the balance, Lock is central to the investigation, but can they trust him to have human interests as his priority in the light of recent events?
Callaghan goes all out in this story, and I was kept teetering on the edge of my seat as the twists and turns culminate in a jaw-dropping finale that is as chilling as it is emotional - one which is so cleverly fore-shadowed earlier in the story. Trust issues keep things interesting, and every member of the team has a vital part to play - plus Kat's son Cam on his trusty bicycle!
I cannot wait to see what comes next from Jo Callaghan, because this has been quite a ride!
Body of Lies is available to buy now in hardcover, ebook and audio formats.
Thank you to The Book Club reviewers group on Facebook for providing me with an ecopy.
About the author:
Jo Callaghan works full time as a senior strategist, carrying out research into the future impact of AI and genomics on the workforce. She was a student of the Writers' Academy Course (Penguin Random House) and was longlisted for the Mslexia Novel Writing Competition and Bath Novel Competition.
After losing her husband to cancer in 2019 when she was just forty-nine, she started writing In the Blink of an Eye, her debut crime novel, which explores learning to live with loss and what it means to be human.
She lives with her two children in the Midlands, where she spends far too much time tweeting, and working on further novels.



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