In this captivating next installment in the Kat & Lock series, the intrepid detective and AIDE Lock, the world's first AI detective, are given their first live case. In Blink of an Eye, the detectives were experimenting with AI by solving cold cases. In this case, they have been given a new case, a live one, and a serial murder at that. When the body of a man is found crucified at the top a mountain, followed quickly by another, the team furiously tries to solve these murders while also keeping themselves from becoming the next victims.

I loved this book, and the previous one in this series--AIDE becomes more and more "human" and charming and an indispensable part of the team, and Kat, while still grieving the death of her beloved husband, is recovering, slowly. The investigative team is also given more space and they are also fascinating.

I hope there is another book in 2025!

Loved it! I’ve been looking forward to reading the 2nd book in the Kat and Locke series. You could read Leave No Trace as a standalone but I really enjoyed In The Blink of an Eye, the first book and would suggest that reading them in succession is the way to go. Having the previously enjoyed the banter between DCS Kat Frank and Detective AI Lock, I found the story’s characters and interactions continued seamlessly. Leave No Trace, Book 2, does not disappoint. Kat and Lock’s new case is a page turner! Finding out who/why someone left a naked man hanging on a cross, to be found sets off the story.
I really like how Jo Callaghan writes- short chapters,researched/fact based info, intrigue with a side of humour- and look forward to her next book.
Thank You to NetGalley, Random House, and Jo Callaghan for the invitation to read and thoroughly enjoy this ARC.

"Leave No Trace" by Jo Callaghan is the 2nd book in her Kat & Lock series. I was able to read an early copy of this book on NetGalley. This novel is a mystery and Detective Kat Frank & AI detective AIDE Lock are trying to solve the murders of 2 men who have been crucified locally.  I enjoyed this book as much as the first one in the series and can not wait for the next one!

Thanks go out to NetGalley, the author and the publisher for the opportunity to read and give an honest review of this book.

After having read the first book in this series, I was very excited to read number 2.

I was very surprised to find the task force of Kat, Debbie, Hassan, and AIDE Locke (my favorite AI crime fighter) ready to tackle their first case in real time. Prior to this, they had worked on cold cases. All of the task members except for Locke, come with their own personal baggage. It makes for a tight team of understanding, empathetic people. They are very supportive of each other. They have become like a family.

The case they are given ends up to be that of a serial killer that hangs the victims on a cross to die of hypothermia. The use of AIDE Locke becomes much more efficient as he becomes an integral member of the team.
The characters with all of their flaws are very likable. Towards the end of this book we see more of humanity in the character of Locke.

This is a very well written series and I cannot wait for the next book in this crime fighting series!

4.5 stars. As much as I enjoyed Callaghan’s first novel “In the Blink of an Eye,” I think that I enjoyed this one even more! AIDE Lock, the world’s first AI detective who can appear as a hologram, continues to gain “personality” and is one of the most interesting literary “characters” I have come across. The entire concept behind this series is very clever and unique, not to mention one that perhaps gives insight into how AI might fit into our world some day. And, exploring another adventure with DCS Kat Frank and her team (including DI Ryan Hassan and DS Debbie Browne) is not only engaging, but is also much like seeing what old friends have been up to recently. I am definitely looking forward to the next in this series!

Leave No Trace is the follow-up to Jo Callaghan's debut novel In the Blink of an Eye, and I have been fortunate to receive both books for free to review.

DCS Kat Frank is back alongside her AI partner Lock. This time instead of solving cold cases, they've been tasked with solving a "live" crime. A man has been crucified and left to freeze to death on a mountaintop, but the killer has left behind no clues. With the combination of Frank's intuition and Lock's ability to quickly sift through data, can their team figure out who the murderer is before he or she strikes again?

I read a few reviews of this book on GoodReads before jumping in, and after reading the whole book for myself, I was surprised at some of the mediocre reviews. Sure, the first book had the original premise of artificial intelligence being used to solve crimes, but this book expands on that and shows just how an AI "detective" evolves, as well as other technology that can be used to solve crimes and save lives. I enjoyed this novel just as much as the first one. It kept me guessing until the end. I really thought someone else was the murderer, so much so that I completely ignored who the real murderer was!

I would recommend this book to book clubs who like police procedurals. You'll get a good discussion about the use of technology, as well as the pressure that society puts on women. And if you're not in a book club, but you like reading about the above things, then I'd recommend this book to you, too!

Leave No Trace is published by Random House and will be available to purchase on January 7, 2025. I received a free e-ARC in exchange for this review.

DCS Kat Frank is working her first live case for the Future Policing Unit with her AI partner, AIDE Lock assisting alongside the rest of her team. The body of a man is found crucified at the top of Mount Judd. They are given their first live case. However the discovery of another man’s body – also crucified – it appears that their killer is only just getting started. It seems that their killer is only just getting started. It is men who are at risk and being asked to be careful and stay at home, Two almost identical murders occurring within days of each other, the Future Policing Unit are under heavy scrutiny, not only from their superiors, but by the public and the press to catch the killer before they strike again and close the case. Will they be able to do it quickly?

The author has written a unique take on a police procedural that works with satisfying results. This is the second book featuring Kat and Lock. This novel is a murder mystery that is rapidly paced and a plotted thriller. I enjoyed the book detectives. I hope that the author will write a series of Kat and Lock. Two novels are not enough. I want more!

4.5 stars, rounded up for this great crime sequel. I liked the first one and this one was even better.

In this installment, Detective Kat Frank, her AI Detective counterpart AIDE-Lock, and their team are given the opportunity to work a "live" case for the first time. Rather than researching cold cases, they are tasked to help investigate and solve the case of a man found crucified on a remote hill in the middle of winter. When a second body is discovered killed in a similar way, they suspect a serial killer may be working the area. Can they uncover who is doing this and why?

I know that some people might find this book a bit too agenda-driven, but I really appreciated the exploration of different forms of vulnerability. I can't give too much detail as it goes too quickly into spoiler territory, but I personally liked the themes of this book. The ever-evolving tech of Lock is fascinating as well, because it shines the light on how confounding human behavior is, and how nuance, sarcasm, and multi-layered meanings of phrases are so complex to comprehend.

If you like a solid police procedural series blended with technology, then you'll enjoy this book. It definitely ends on a cliffhanger so I'll be interested to see what she comes up with next.

LEAVE NO TRACE
Jo Callaghan


“In the beginner's mind, there are many options, but in the experts, there are few.”

Shunryū Suzuki

What aspects of being human could not be replaced by artificial intelligence? How can we use AI when our aptitude is lacking to forge a new future alongside our creation?

LEAVE NO TRACE follows Inspector Kat Frank and AIDE Lock, her artificial intelligence officer. Aide is a hologram manifested from a watch-like attachment on her wrist. It is up to her to activate the hologram and decide when it is used.

They are on their second case together as partners and this time they are set to solve a gruesome murder in the dead of winter. A man has been crucified on a cross atop a hill. Not just any hill. A hill made of waste at their local recycling and waste station.

It happens deep in the frigid winter months and traversing to the top of the hill is a significant part of the trouble in solving the crime. They must enter and exit the scene as if they didn’t. They must solve the crime and LEAVE NO TRACE.



This is the second book in an incredibly interesting crime fiction series written by Callaghan. I read the first book in the series last year and loved the questions it raised and the thought-provoking situations our characters found themselves in.

The dynamics would be interesting with any type of plot, but I find it more so within the context of a crime fiction novel. It seems perhaps that one of the first ways AI will be used would be in crime prevention and investigation.

The book is excellent first because of the writing and second because of the context. There are several situations these partners get into where the strengths and weaknesses of each partner are explored.

There are obvious advantages to having AI investigate crimes but there are also many disadvantages and key oversights that need to be addressed.

Coded in probability when put in situations where there is only one viable option, we as humans are superior in our ability to hold several possibilities in one mind. Several opportunities in one hand.

Sometimes you do what needs to be done, sacrificing what is perfect for what is right.

Excellent conversations and I can’t wait for the next in the series. 10/10 recommend!

Thanks to Netgalley, and Random House Publishing Group - Random House | Random House Trade Paperbacks for the advanced copy!

LEAVE NO TRACE… ⭐️⭐️⭐️⭐️⭐️

DCS Kat Frank and her AI counterpart, AIDE Lock, are back and no longer solving cold cases, but are tasked with solving an active murder case with a rather bizarre twist. The dynamic between Kat and Lock is, at times, humorous, but their working relationship also exemplifies the vast differences and limited capabilities of both humans and machines. Their combined efforts, however, turn this imperfect coupling into a really great investigative team. Hence, “Leave No Trace” is yet another compelling police procedural that I found amusing and enthralling from beginning to end. I absolutely love this series, and I can’t wait to see what this author has in store for Kat and Lock next.

4.5 stars
DSC Kat Frank has been partnered with an AI detective, Lock, as part of a pilot program. In the past, they've only worked on cold cases together, but this time they are working on a current case with a high profile. Not only is Kat's job on the line, but more lives are at risk. I love how well Kat and Lock work together and that at times you can tell that Kat considers Lock even though he isn't human.

The book does a great job of balancing the case, the issues which come up regarding the use of AI, and the personal lives of Kat and the others on her team. Kat and her son are both grieving the loss of Kat's husband so the growth she is showing, and the touching endings are both fantastic and set this book apart from other mystery/thrillers. I loved both this book and the first book in the series (In the Blink of an Eye, which I highly recommend), and I am already looking forward to reading the third book in this series when it comes out.

I received an advance copy of this ebook for review consideration from NetGalley and Random House, but my review is voluntary and unbiased.

Unfortunately I didn’t realize this was a second in a series. I liked the idea of an AI detective pairing with a police department to solve a crime. Unfortunately the plot never seemed to come together for me. Thank you to NetGalley for the chance to read and review this book.

DCS Kat Frank, a twenty-five year veteran of the police force, is the head of the FPU, Future Policing Unit, in Warwickshire, England. One of her responsibilities is to make use of AIDE (Artificially Intelligent Detecting Entities) Lock, a groundbreaking invention that its creator, Professor Adaiba Okonedo, believes will make law enforcement more scientific and evidence-based. Although Kat and her boss are skeptical about the value of AI in combatting crime, during their last case, Lock was an invaluable partner who helped Kat nab the culprit and save lives. In Jo Callaghan’s “Leave No Trace,” Frank and her colleagues, DI Rayan Hassan and DS Debbie Brown, will turn to Lock once again to help them track down and apprehend a serial killer.

Callaghan is a strategist and researcher who is an expert in the field of AI, so she knows whereof she speaks. She follows up her excellent debut novel with another suspenseful, well-constructed, and powerful tale that explores the ways in which various individuals process trauma and grief. Kat is a lonely widow who mourns her late husband, John, particularly during the winter holiday season. She throws herself into her work, partly as a distraction from the tremendous void in her life. DCS Frank and her team identify the first two victims, both male. One was engaged to be married, and the other had a wife and two children. The detectives interview friends, family, and others who may have useful information to share. In addition, the police, assisted by AIDE Lock, examine the physical evidence, check phone records, and view CCTV footage.

Lock is a standout character in this thrilling novel. He appears as a hologram when Kat activates him, and she is amazed at his ability to sift through reams of data at lightning speed. He is also, at times, unintentionally funny, as he puzzles over the irrational nature of human beings who rely on emotions to a far greater extent that he thinks is wise. The plot is far-fetched but compelling and imaginative, and the dialogue is sharp and fast-paced. The author sensitively addresses such issues as the victimization of women; vengeance as a double-edged sword; and everyone’s need for companionship, love, and empathy in a world that is too often cold, brutal, and unfair.

An AI Sales Pitch in a Fear-Mongering, Through Confusion, Fiction

Jo Callaghan is an AI researcher, who managed to sell a bestseller as her first book a few months earlier in 2024, and has already released this second part in what is a semi-series because the topics are related.
A “…thriller that pits algorithms against experience, logic against instinct, and one undetectable killer against two extraordinary detectives.” This blurb suggests that this is a techno-thriller, but this is the opposite of the feel generated by its opening pages. They just describe a person walking in a “stupid” fashion because he’s not paranoid. Somebody is standing in the freezing cold outside looking at a dull house, and dull things happening in it. The whole thing is written as if this dullness is horrific. The chapter stresses this horror-genre feeling by closing on the word “fear”. In the next chapter the problems continue. Basically, the author refuses to reveal what is going on, why it is happening or why the reader is repeatedly told to be scared, without being told “of what?” To check if anything in this book is as-promised, I searched for “algorithm”. It appears a couple dozen pages in, in a long paragraph that explains some things. “…McLeish was still hostile to Artificially Intelligent Detecting Entities, afraid they’d become a Trojan horse for yet more cuts to police numbers…” Kat’s “late husband’s cancer had been misdiagnosed by AI”. The author of this book, Callaghan, had a husband who died of cancer, and such mentions seem to be intended to be autobiographical. The previous points are a rare clear moment. Then, comes the mention I searched for: “Lock’s algorithm-led approach could often be exasperating…” Lock is the investigator’s “AIDE” or “AI partner”. No explanation just what algorithm this is referring to, or how an “algorithm” is not a synonym for “AI” in this context. Later on, there are echoing passages that juxtaposition the character’s “gut feelings” against “Lock’s fact-based algorithms”, as if these are the serious options for curing cancer, as opposed to it being a difference between human research, and algorithm-assisted human research.
“When the body of a man is found crucified at the top of a hill in the British Midlands, AIDE Lock—the world’s first AI detective—and Detective Kat Frank are thrust into the spotlight as they are given their first live case. When a second body is found, the police issue an extraordinary warning to local males aged between thirty and forty years old: • Avoid drinking in pubs. • If you insist on going to a pub, do not leave alone. • And definitely do not leave a pub with a stranger./ With the national media and local men in an uproar, Kat and Lock have to combine their instincts and algorithms to catch the killer before they can strike again.”
There are some structurally interesting interview chapters later in the book, where whole chapters include the Aristotelian interview format, with minimum explanations of how things are being said. Though these interviews are discussing mundane things about drinking coffee, and walking around that seem irrelevant to solving the crimes at-hand. The larger problem is that the nature of the crimes is weird, but seems entirely unrelated to the necessity for specifically an AI detective being put on this case. It is frightening how little sense this whole novel makes. The hysteria and the mania about AI makes as much sense. Why are people investing in AI, when its common uses (like generating an auto-image, or a robot-chat) are probably going to be given away for free? This seems to be a case of an AI researcher investing in publishing a novel just to help her large propaganda effort to sell AI to more investors in this sector…
—Pennsylvania Literary Journal, Fall 2024: https://anaphoraliterary.com/journals/plj/plj-excerpts/book-reviews-fall-2024

Jo Callaghan’s first novel was easily one of my favorite crime stories of 2024. All of the elements that made me love that book are back in Leave No Trace, the second in this series. These include characters with depth (and backstory), a plot that keeps the pages turning, and the use of a unique sidekick to detective Kat Frank.

AIDE is an AI created detective. Through a hologram, he looks very real. His thoughts, although at times concrete because of a lack of understanding of nuance, are often key to the case. It has been enjoyable to watch the “relationship” between Kat and AIDE evolve. That is just one of the joys of the series.

This time, Kat has asked for a “live” as compared to historical case. The one that she is given is rather grim. A man has been found at the top of a local landmark and he has been gruesomely murdered. The case will lead to fear and warnings to young men.

Readers know that the case will be solved. The enjoyment is in watching how the team accomplishes this.

Kudos to the author. I am already eager for book three.

Many thanks to NetGalley and Random House Publishing Group for this title. All opinions are my own.

A team of detectives with an unusual asset confronts a horrible crime

As the Christmas holidays approach DCS Kat Frank is on the edge of depression. She lost her husband unexpectedly the previous year, her son has left their home to attend university, and she is rattling about the house alone. Her work is her tether to the real world and she pushes her boss to assign her and her relatively newly formed team, the FPU (Future Policing Unit) a real case rather than the the cold cases they have to date been given. Her four member team is unique in that her partner Lock is not a human partner, he is an AIDE (Artificially Intelligent Detecting Entity), and this partnering of an AIDE with a team of detectives is a new experiment. Although initially reluctant to expand the team's remit to working a live case (as he is somewhat hostile to the concept of AIDEs, fearing that they will replace rather than enhance existing police personnel) her boss relents when the dead body of a young man is found naked and gruesomely displayed in an isolated area. With little in the way of forensic evidence and no clear motive (could the killer be the victim's fiancee, or perhaps someone from his professional life?), this will prove to be both a frustrating and a highly visible case for the FPU, especially when another dead body is found similarly displayed. With public perception mixed on whether having an AIDE involved is wise and fears of a serial killer on the loose are putting the area on edge, the pressure is on from all sides for the team to identify a suspect and make an arrest ASAP...but Kat isn't convinced that any of their suspects are actually guilty of the crime despite what Lock's algorithm indicates. Data driven logic clashes with instinct and experience...can they find a way to incorporate both sides in time to prevent another killing?
Leave No Trace is a fantastic thriller, a classic British detective story with a. contemporary twist. As we all come to terms with the growing presence of AI in each of our lives, whether or not we like the concept or understand how it works, here the reader is presented with the ethical questions, practical limitations and amazing possibilities that such a tool could bring to policing. Lock can comb through hundreds of thousands of social media posts in seconds, saving the countless hours of human effort needed to achieve the same results, but the search is ultimately only as good as the instructions given. Kat herself has reason to distrust the efficacy of AI (her husband was initially misdiagnosed by someone using AI as a diagnostic tool, and the delayed diagnosis and treatment may have contributed to the ultimate failure to save his life), but also has Lock to thank for saving her son's life during a previous investigation. Many issues currently faced by law enforcement in the UK and beyond...diversity in the workforce, perceived lack of transparency and inequities in the way situations are handled depending upon the identity of the victim and/or perpetrator to name a few...are woven into the plot One of the team members and the professor who created the AIDE have each had less than positive experiences with law enforcement and bring their own reservations and biases to the job. Interesting and well-developed characters and a gripping mystery combine to form an excellent novel, and with it a fascinating premise. This is the second book in the series, but it can easily read as a standalone. Readers of authors like Jenny O'Brien, Val McDermid and Imran Mahmood should add this book (and its predecessor In the Blink of an Eye) to their list of must-reads, as should fans of well-written crime novels. While the topic of AI is prevalent in the story it did not feel to me to be science fiction, so those who are not usually readers of sci-fi should not dismiss this book on that score. I thoroughly enjoyed reading Leave No Trace, found it difficult to put down, and eagerly await another installment in the Kat and Lock series. Many thanks to NetGalley and Random House Trade Paperbacks for allowing me early access to this smart and intricately plotted tale.

If Jo Callaghan's first novel featuring AIDE Lock and DCI Kat Frank, In the Blink of an Eye, was a stand alone, I would have been happy. The fact that it's a continuing series with the brilliant followup, Leave No Trace, I am ecstatic! The murders that the plot centers on are inventive and dark. AIDE Lock is clearly on a learning curve about how to use its vast resources and also understand the intangible human intuition that drives much of DI Frank's investigative process. This novel shows AI's promise as well as its limits (particularly in the physical world). There are side plots as well, most of which are carryovers from the first novel: Kat's rocky relationship with son Cam, DS Browne's coming to terms with looming single motherhood, and DI Rayan Hassan's ambition.
Callaghan is very good at the subtle drop of a clue that the perceptive reader might catch, even if Kat's team misses it, and who doesn't love the feeling of being slightly ahead of the murder team in solving a case?

Another solid thriller by Jo Callaghan! I was excited to see this book because I wanted more from our favorite Detective/AI duo. I enjoy their relationship, especially as AI Locke attempts to figure out the nuances of his human partner.

The mysterious deaths kept me guessing and while it may not be everyone's cup of tea, I do enjoy a good police procedural. I think this works as a standalone but is much better if you have read In the Blink of an Eye first. I am looking forward to see where the next book takes us!

Thank you to NetGalley and Random House Publishing Group for the advanced copy in exchange for my honest review.

In the first book in this series, In the Blink of an Eye, we were introduced to DCS Kat Frank of the Warwickshire Police. When she returns to work after a long absence, she is essentially coerced into accepting the offer of leading a pilot project for police investigations to incorporate an “AIDE” as a team member. AIDE stands for Artificial Intelligence Detecting Entity.

The AIDE program was created in cooperation with Dr. Sophie Okonedo, who has, from family history, a lot of distrust of police methods, viewing them as being dominated by prejudice and other invalid assumptions. She developed an AIDE she calls Lock, thinking that AIDEs can replace the status quo with objective rationality.

You know how they say conflict is necessary to make good fiction? Well, Jo Callaghan must fervently believe that, because in the first book, Kat and Lock are constantly at odds. Sure, Lock steps on toes with his stats-based approach and complete lack of emotional intelligence, but Kat does want to spend any time helping Lock learn. (By the way, I call Lock “he” because when he occasionally projects himself as a hologram, he tends to use Chadwick Boseman as his avatar.)

The pilot project turned into an active crime investigation and, after the case is wrapped up, Kat and Lock are starting to make a working partnership. That brings us to this followup, Leave No Trace. Thankfully, the conflict dial has been turned down a bit. There isn’t nearly so much hostility from Kat toward Lock and Dr. Okonedo toward all of the police. Instead, Kat has learned to take advantage of Lock’s power in data retrieval and analysis and, while he still takes his shots at Kat’s feelings and hunches, he is beginning to see that they are actually the result of years of experience.

The crimes in this book are pretty over the top. One man, and then another, are found naked and hanging from a cross on top of a hill in the middle of winter, both deal from hypothermia. But how did they get there, and why? A solid police procedural follows. I thought this was better than the first book in the series, though I think both books could stand to be tightened up a bit.

A good addition to the rapidly expanding collection of AI driven stories....some of the murder details were a bit gruesome for me but overall an entertaining story!