I liked this semi sci-fi take on modern police work using an AI hologram that can calculate statistics, scan thousands of photos and articles in an instant, all in aid of solving crime. The mystery was interesting though a bet far fetched, and the developement of some self awareness in the hologram was interesting and slightly frightening… you can see how this possibility can go to extremes.

The first novel in this series, "In The Blink Of An Eye" made my favourite reads of 2024 list. "Leave No Trace" will, no doubt, make my favourites of 2025 list! My first reaction? Brilliant! I loved it, and can't wait to read the next book in the series!

The characters were so well drawn and the police investigation so compelling, that I couldn't turn the pages fast enough!

Detective Chief Superintendent Kat Frank is a forty-five year old widow and the mother of a teenage son. She lost her husband to cancer just a year ago and her grief is still raw. It is coming up to Christmas and her teenage son is away at university, so Kat feels a loneliness she had never anticipated. Her boss puts her on her new team's first LIVE case! Once again, she is to work with an AIDE Lock (Artificially Intelligent Detecting Entity). Her team will include four people if you include the AIDE.

AIDE Lock - is a wristband around Kat's wrist. However, 'he' can be made to look human via hologram. When he is, he is a tall, slim black man. Think Idris Alba with slight touches of Spock.

Detective Inspector Rayan Hassan - is a smart dresser with a law degree and a high conviction rate. He challenges Kat's authority at times and they lock horns on occasion. Rayan is a good friend to his partner DS Debbie Brown. He is smitten with Professor Okonedo, who is in charge of AIDE Lock.

Detective Sergeant Debbie Browne - is a twenty-four year old who has been with the Warwickshire Police for six years. Though a very diligent officer, Debbie has little self-esteem and is constantly apologizing. She is single, and is eight months pregnant. She worries that her condition and imminent life changes will impact on her long sought after career.

Professor Okonedo - a brilliant though diminutive Asian woman with a chip on her shoulder and a huge grievance against the police. She blames them for her brother's unjust incarceration. Though not official a member of the police, she is AIDE Lock's 'handler'.

Up until now Kat and Lock have been working cold cases. Now, Kat and Lock's first live case involves a crucifixion. A young man has been left to die of hypothermia while tied to a crude cross. Just four days after this, another young man suffers the same fate in another isolated location. With intense pressure from the higher ups and the national and international press, Kat and Lock strive to find the perpetrator. Kat's keen sense of justice, her strong moral and ethical compass, and her high-principles, all serve to make her boss, and AIDE Lock, sometime shake their heads.

With themes of gender role, the emotional after-effects of trauma, artificial intelligence, and personal bereavement, this novel was a mesmerizing read. Machine vs. human. How far away from this premise are we really? Not far I think. Machines can make decisions based on facts and algorithms, while humans can make decisions on 'gut instinct'.

The author has taken some elements of her own life and incorporated them into the book - lending the narrative a ring of authenticity.

When reading the pronouns of some of the characters I became a little confused. The pathologist has pronouns of they/them and when reading a sentence, it can be off-putting to those of us who are 'old-school'. I thought it was very amusing when Lock stated his preferred pronouns were he/him. Kat always refers to Lock as 'it', though when he was asked, he said he wants his pronouns to align with his holographic presentation.

I really came to care for all of the characters and I'm eager to learn more about them in the next book. Lock in particular, seems to be becoming more human and the scenes with the horses and the baby were very poignant. I empathized with his plight.

The ending was outstanding and made me SO eager to read the next book "Human Remains". Highly recommended to all fans of well written police procedural fiction.

“Leave No Trace” by Jo Callaghan, the author of 2023’s “In the Blink of an Eye,” offers a thrilling ride with a twist of tech. Detective Kat Frank teams up with AIDE Lock, the world’s first AI detective, to tackle their wildest case yet — a gruesome crucifixion that’s just the beginning. As Kat’s gut instincts clash with Lock’s razor-sharp algorithms, the duo races against time (and each other) to stop a killer with a terrifying agenda.

Packed with tension, dark humor, and provocative AI ethics, this mystery keeps you guessing and grinning. If you’re into gripping crime, quirky partnerships, and a dash of sci-fi, this book is your next obsession.

Detective Kat Frank and her AI partner Lock are in the spotlight for their first live case, when a man is found crucified on top of a hill. When a second one is found, men are warned to avoid drinking, going to pubs alone, or going home from a pub with a stranger. Local men are in an uproar with this advance, and the national media following the case, the detectives must find the killer before they can strike again.

Leave No Trace is the sequel to In the Blink of an Eye, which introduced AIDE Lock and Detective Frank. They've closed other cold cases and now are in the thick of tracking down the killer in a sensational murder. They go the usual route of checking on friends, fiancée, and business deals; Lock provides some help but also sensationalizes the investigation further when a local reporter mentions its involvement. As with any murder investigation, there are competing directives: find the killer, inform the press, satisfy the public, and be transparent. We certainly see this clearly here, especially when the second body is found and the press goads Lock into warning men to stay indoors as Kat once warned women to with a prior serial killer.

The story increases the tension for Kat and her team. Debbie's close to her due date, Rayan is ambitious and has a crush on the professor, Kat is still grieving and now an empty nester, and there's incredible pressure on their program for its AI use. Police follow what few clues they have, and we see what they're up against. There's a balance in the story, as we follow Kat and the pressures in all directions, as well as the actual murder. The motive is hidden, and the killer is working through trauma. The story is heartbreaking on all fronts, and very well written. At the end is a possible teaser for a third novel in this series, which likely will be just as tension-filled and exciting.

Leave No Trace is book two in the Kat and Lock Series by Jo Callaghan.
I enjoyed book one In the Blink of an Eye. So I was looking forward to jumping to into the second title.
This crime thriller was so, so good.
The storyline is full of twists and turns that will keep you guessing
A compelling British police procedural.
Author Jo Callaghan builds the tension to such a high every step of the investigation to the point that I could not put this book down and kept reading late into the night.
I can’t wait for book three Human Remains.

Thank You NetGalley and Random House for your generosity and gifting me a copy of this amazing eARC!

This book was dark, gritty and a really interesting read!

"Leave No Trace" was a solid follow-up to book one in the Kat and Locke series. I find the AI / Human partnership to be such a unique and intriguing concept. This storyline was a bit more gruesome than the last but the author's skillful storytelling still had me turning pages.

I'm looking forward to seeing what will happen in book three!

Thank you Jo Callaghan, Net Galley and Random House Publishing Group for providing me with an ARC of this book.

Many thanks to NetGalley and Random House for gifting me a digital ARC of the second book in the Kat and Lock series by Jo Callaghan. All opinions expressed in this review are my own - 5 stars!

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. Then a second body is found dead in the same manner, and suddenly the team is thrust into the media spotlight.

I was a huge fan of the first book in this series, In the Blink of an Eye, and recommend you start with that to learn the backstories of these characters, even though you could definitely read this as a stand alone. Lock reminds me of Data from the Star Trek series - can make calculations in the blink of an eye but struggles to understand human emotions and gut reactions. Kat is still struggling with her empty nest and heart after the death of her husband and their son's departure to college. I love all the members of this detective team and it was so fun to get reacquainted with them and watch them investigate these horrific murders. This is definitely a nod to the near future as AI seems to be integrated more and more into our world. I especially thought the virtual autopsies were fascinating. Can't wait for more books in this series - highly recommended!

Make sure you read In The Blink Of An Eye first!!!

With that out of the way, Jo Callaghan is quickly becoming one of my favorite authors! Knowing it's speculative fiction, it doesn't read like scifi at all. This is very much a police procedural/mystery, and that's a compliment. Her integration of an AI character (Lock) takes nothing away from the bones of the story and adds a unique voice and perspective to a genre that can, at times, be repetitive. Incredible, once again.

This is the second book in teh Kat and Lock series and the first one was a winner for me, so naturally I picked this one up.

Description:
One detective driven by instinct, the other by logic.
It will take both to find a killer who knows the true meaning of fear . . .

When the body of a man is found crucified at the top of Mount Judd, AIDE Lock – the world’s first AI Detective – and DCS Kat Frank are thrust into the spotlight as they are given their first live case.

But with the discovery of another man’s body – also crucified – it appears that their killer is only just getting started. With the police warning local men to be vigilant, the Future Policing Unit is thrust into a hostile media frenzy as they desperately search for connections between the victims. But time is running out for them to join the dots and prevent another death.

My Thoughts:
There were horrific, gory murders in this book. I have to admit, the crucifixtions turned my stomach, so if you are sensitive you may not want to read this. The AI Detective Lock feels so human I felt like he was a person with feelings. Nevertheless, Kat needs to help prove that AI can assist the department in current investigations, so this is the first one for Kat and Lock to work. The investigation is intense and I couldn't put the book down. It's amazing what AI can do, but we certainly need human views to reach good conclusions. This does show how AI could be an asset in police work. I highly recommend to anyone interested in AI or who enjoys police procedurals.

Thanks to Random House through Netgalley for an advance copy.

Wow. While this will be most appreciated by those who read In the Blink of an Eye, it's a cracking good read even as a standalone. DCS Kat Frank and AIDE Lock have a live case this time out, having proved themselves on a cold case that went hot. It's just before Christmas, it's snowing and someone crucified a man and cut off his ears-and everyone they interview lies to them about something. Luckily, Lock's ability to sort through masses of data and DS Debbie Browne's ability to to find the nuances combined with DI Hassan's doggedness and well, Kat, means that the villain won't get away with this. Or with- wait-no spoilers! This is topical and clever and I like how things wrap back to one another. I'm also a huge fan of all of these characters-especially Lock who is beginning to learn human behavior, sort of. While I was a skeptic about Lock in the first book, he's grown on me (and yes I recognize how implausible he is). This series was born out of tragedy and my condolences to Callaghan. That said. Callaghan should be proud of what she's created. Thanks to Netgalley for the ARC. The writing is great, the plot moves quickly (it's a page turner!) and I'm really hoping for another one.

When Detective Frank starts using an Ai detective called Lock, thing start to take a turn. Frank previously had Lock as part of a collaboration and the Ai detective was able to solve other cases. When a man is found crucified at the top of a hill and then another is found crucified in a filed things start to take an ugly turn. There is no way to know what is coming next. Will Lock and Frank be able to solve this case?

This book was such a great read! When I first started it I wasn't so sure about the Ai component and how that would play in. I didn't want it to be something where we go into Ai and science fiction. I wanted more of a thriller and that is what I got. The lessons that also came from this book in relation to the use of Ai and personality and feelings is something we all should listen. I thoroughly enjoyed this book and was left wanting another book!

This is the second book in the Kat and Lock series. Jo Callaghan has created very likable characters with these two. One is a female DI and the other is an AI who they are trying to use in the course of investigations.

In this book Kat and Lock are looking for a suspect who has hung a man on a cross and removed his ears. Who would do such a thing. His fiance possibly? Maybe his best friend? Or is something much more sinister at play?

When Kat gets the call about a man being found hung on a cross she immediately starts trying to figure out what happened and why it happened. Before it happens again. In four days it does happen though. Her boss of course doubts her ability to solve the case but she doesn't give up. Kat has a wonderful team and they are all working overtime to solve these murders.

A reporter is letting people know things before Kat can get a handle on things. Kat wants this solved before another murder can happen. Her partner, the AI, is working with her by looking at videos and reading everything as fast as he can.

I have to say that this was an excellent book. A first rate follow of the first book, In The Blink of An Eye. You get to know more about each character and how they work. How well they all get along. While I did figure out who the killer was and why it certainly did not take away from the story. Not in the least. I was on the edge of my seat when things came to a head and Lock(AI) was talking to the murderer. And at a few other times I found myself holding my breath. I also cried a few times. This book was so good but also needs to come with a trigger warning for sure. It contains talk of a rape, a drug induced rape. Date rape drug use and other things. But it's still a wonderful book and well written.

This author has a series here that I believe will keep getting better and better. I'm looking forward to the next installment already.

Be sure and read the Acknowledgments at the end as it contains some info. My heart goes out to this author and her family.

Thank you #NetGalley, #RandomHousePublishing, for this ARC.

Five big stars.

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.