I liked this FBI investigative novel, mostly because of the quirky characters. Each agent has been placed in this unit because of some previous unacceptable behavior. Each one has some unique ability, such as an eidetic memory or amazing sharp shooting skill, and they work through this case differently than a traditional team. Their expertise involves pattern recognition so their methods are as unique as they are. The banter between the agents was entertaining.

I had mixed feelings about the lead character, Gardner. He was so sure of himself, every time they got a new clue he was quick to conclude this person was their villain. I would have preferred he have a more open mind as he was wrong, until the last one. It was irritating.

The plot was suitably complex as it involved past crimes and present people in the FBI. We got a good sense of the politics within the agency as the agents go about their unusual ways to solves the murders. I do like McMahon's writing style and will be watching for the next book in this series.

I received a complimentary egalley of this book from the publisher. My comments are an independent and honest review.

PAR Unit #1. The PAR (Patterns and Recognition) Unit is a special branch of the FBI staffed with analytical geniuses who do not see the world as ordinary people do but gifted with skills to solve puzzles and see outside the box. When DNA results in a recent homicide come back as belonging to a serial killer thought killed in a fire years ago the unit is called in. Subsequent deaths cause the team to believe they are searching for a vigilante with a mission to hunt down criminals who somehow escaped justice. This investigation will take them out of their usual working behind the desk situation into the field as leads send them across the country. Agent Gardner is an isolated self contained protagonist who must get more in touch with his human side to coordinate his team and follow leads. The supporting cast of characters are quirky and diverse yet committed to justice. The story line is compelling and dramatic with unique conflicts and twists that keep the momentum moving at a fast pace. The forensic and investigative details seemed to be authentic. I have long been drawn to FBI thrillers especially those relating to serial killers and I found this premise of a special branch to be fresh and engaging. This is listed as #1 so I am looking forward to the next adventure from this group of talented detectives and am eager to learn more of their back stories. I enjoyed the interaction as the newly formed team learned how to work together and play on each others strengths. If you enjoy a tense and dark crime novel this is one to dive into.

This was such a great book! From the first chapter, I was hooked. It definitely felt very much like Criminal Minds both in the characters and the story.

Head Cases is a twisty police procedural that was like putting a puzzle together. Everything slots into place bit by bit until the full picture becomes clear.

I'm thrilled that this is going to be a series. Gardner, as an analyst, was a wonderful character. His memory recall and pattern recognition skills were a great asset to this story. This was a fantastic start to a new series and I can't wait for the next installment.

I received a complimentary copy of this book. Opinions expressed in this review are my own.

I really enjoyed listening to this. The narrator was the perfect choice for this. He sort of gave me Joe Kenda vibes. Head Cases is the perfect book for those of us who love to watch police procedural and detective shows. I think it would also be great for true crime readers who want to stay close to the genre but take a break from real crimes! I myself am a true crime lover at my core, but I also really love thrillers and mystery. This sort of blends those loves for me, while not a true crime case it definitely feels like it could be at times.


Overall, this was a brilliant story that kept me interested and on the edge of my seat. I was even shocked by many of the twists. I can't wait to see where this series goes. I'm definitely going to be eagerly awaiting book twos release.

I received a copy in exchange for an honest review.

This was my first novel by John McMahon and he will now be an author I look for! A group of FBI agents are hunting down a murderer that is seeking his own justice. This novel kept me on the edge of my seat the entire time. I would highly recommend.

The Patterns and Recognition unit of the FBI, also known as PAR, takes on the cases that others cannot solve. Consisting of a mathematician, a computer analyst and an expert in weapons, and led by a career agent, this group focuses on cold cases with the hope that they will see things that others have missed. Agent Gardner Camden is a member of PAC, and he and the team find themselves embroiled in a new case. A man has been murdered, yet his DNA links him to a serial killer presumed dead many, many years ago. When a second murder follows and a pattern emerges, the team is in a race to find the killer before another bad guy ends up dead.

Head Cases had me intrigued right from the beginning. While taking place in modern times, parts of it had an old noir/crime show feel to them–those are some of my favorite genres–and the narration by Damron only contributed to that feeling. It was almost like I was listening to a crime drama on the radio. There is such a variety to the characters and each one adds their own flavor to the team and to the story. Many of the twists and turns caught me by surprise, keeping me guessing until the end. I absolutely cannot wait for the next PAR Unit novel and I hope Damron narrates that as well!

Really great read, perfect for anyone who was a fan of Reid from Criminal Minds. Very suspenseful and engaging

Serial Killers!!! wow this book was so good. FBI’s Patterns and Recognition (PAR) unit is generally tasked with solving cold cases is hunting down a prolific serial killer. This is book 1 in what I'm hoping becomes a series. I LOVE CAMDEN

This book reminds me of criminal minds - and it had me engrossed.

It's well paced and keeps you guessing.....

Please let there be a book 2 of the PAR unit and Camden.

5 stars! Great read! Loved every minute!!! Thank you to NetGalley and the publisher for the free ARC in exchange for an honest review!

Gardner Camden and his band of misfit agents make up the PAR (patterns and recognition) unit of the FBI. On the verge of being shut down, Camden has one last chance to save the unit and his career by capturing a serial killer hunting serial killers, but this killer seems to know the FBI's every move.

You ever read a book where you get low key mad when you have to stop reading and take care of your responsibilities?
Head Cases did that to me.

I like law enforcement thrillers and this was very well written. I was hooked early on and loved the unique team with their own special skills. I did not see the twists coming, this book was a fun ride.

The acknowlements notes that this is part of a 2 book deal, and I am excited to get my hands in the second book in 2026. Thanks to @netgalley @minotaur_books @johnmcmahonbooks for the arc in exchange for an honest review.

It’s still the first month of the year but I already know I just read what is going to be one of the best books I read all year and that I’ve found an author whose work I will read more of. The Patterns and Recognition (PAR) unit of the FBI is comprised of a team of agents with unique, individual skills, all are smart and skilled, quick to find and understand clues, patterns, and trends. They are also quirky, and have unfortunately likely had a blow up or run in somewhere along the line in their careers that resulted in them being placed in the PAR. They are often looked at with disdain by the “regular” FBI and referred to as head cases – or worse – by other agents.

The PAR unit is usually given the unsolvable cases. In Head Cases they are following a murderer who believes what he is doing is a good thing, eliminating bad people, providing justice. From the start the case is complicated and baffling. The first victim is a serial killer thought dead for years. That discovery is only the tip of the iceberg, and from that point it only gets more complex and convoluted, and confusing for the PAR agents working the case. As layers are uncovered things that were thought true are now false. There is a web of connections but so much has been misdirected.

The story is told through the eyes of Gardner Camden, an analytical genius with an affinity for puzzles. Not so much a genius at personal relationships and communication, however. He’s made team leader. His instincts are spot on; his methods of getting the point across to his team not so much so. He’s a fascinating character that gives the story depth. He has codes and constraints and rules and is firm in them, so much so that he turned his then-wife in for wrongdoing and she is currently in prison. He’s close to his 7-year-old daughter but she lives with a grandmother. His own mother is in a nursing home, sometimes aware and sometimes not. Author McMahon does an outstanding job of taking us back through Camden’s history to better understand him while also displaying his excellent analytical skills, and yes, even good team leader skills.

Head Cases has so many layers, so many parts, so many things you don’t even think of but that make perfect sense. It’s fast-moving, expertly plotted, suspenseful and complex but with solid clues, a totally unexpected twist and a very satisfying ending. It was a pleasure to read, to try and keep up, make educated guesses and absorb all the information the agents have to work with. Thanks to St. Martin’s Publishing Group for providing an advance copy of Head Cases. I thoroughly enjoyed it, recommend it without hesitation and hope this will be a series. I voluntarily leave this review; all opinions are my own.

Thank you Netgalley for giving me the opportunity to read and review this book. The opinions written are completely honest and my own..

I'll admit I was on the fence about reading this title and I'm extremely glad I went for it.

The on reaso it took me more then a week to finish it is because I am reading multiple books. This is one of those books that begs for you to to keep reading. The character and plot setting, dragged a bit, but once that was out of the way I found the beginning of my new favorite series.

A serial killer that’s hunting serial killers?! Say less.
I devoured this book in one day. I couldn’t put it down and when I absolutely had to put it down I listened to the audiobook. This book is the first in a brand new series featuring FBI agent Gardner Cameron and a team of agents that make up the FBI’s PAR (Patterns and Recognition) unit. They’re nerdy, quirky, unconventional and brilliant. They all have a record of misbehavior that landed them in the “misfit” group. This unit is called in when all others have failed to solve a case, typically from their office and not out in the field which is exactly where they end up hunting a killer that’s murdering killers. If you’re a fan of Criminal Minds, Mindhunter, CSI this is for you. It’s fast paced, twisty, and has great character development. I loved everything about it. I can’t wait for another book! I’m

This book was given to me by NetGalley to review. I enjoyed this book and will probably read the sequels. It did get a little repetitive that Gardner thinks differently than everyone else, but I also find it endearing.

Thank you so much to NetGalley and John McMahon for providing me with a complimentary digital ARC for Head Cases coming out January 28, 2025. The honest opinions expressed in this review are my own.

This is the first book I’ve read by the author. I received it directly from NetGalley. It’s not something I would normally choose. I really love murder mysteries and thrillers, but I don’t enjoy FBI stories as much. It was a good story. I liked it. Gardner is a good character. I just wasn’t obsessed with it. I would check out other books by this author.

Head Cases is a complex, smart mystery with great characters, good pacing, and an original plot. What more could you ask for?
The FBI's Patterns and Recognition (PAR) unit is a group of smart and super-talented agents who take on cases that other units can't solve. They've all screwed up something somewhere to be assigned to the PAR in the backwater of Florida, including PAR member Agent Gardner Camden, an analytical genius who doesn't do personal interactions very well. The team is assigned to a case where it soon becomes apparent a serial killer is killing serial killers and only the PAR has the skill set necessary to bring them to justice (or at least try). The author's notes at the end say Head Cases is part of a 2-book deal, which is great, but I suspect I won't be satisfied with only two!

This is literally if Criminal Minds was a book and I was so here for it. I think this is one of my most unique reads of the year, and I just ate it up.

Highly recommend if you are a fan of criminal shows with an emphasis on how the human mind works.

Thank you to Netgalley & The publisher for my early e-arc.

What happens when you get a bunch of neuro-divergent FBI agents together? You get PAR - the Patterns and Recognition group. Head Cases by John McMahon gives us a group led by Cameron Gardner, put in charge of finding a vigilante serial killer out for justice.

"Cameron Garner works in the Patterns and Recognitions group for the FBI. He gets called to the murder scene of a victim he and the rest of the FBI thought was already dead - someone who was a serial killer. After another serial killer victim is found, Gardner and his team know they're after a different kind of killer."

This group of agents is different ... and often misunderstood. But they are agents out to solve whatever crime they're asked to solve. They're unique ways of looking at problems is an asset to catching the bad guys. Cameron knows that his filters are not always considered normal, but he works to keep his comments appropriate. It's fun being inside his thought processes.

Wild ending to this one - and proof that it's great to have someone called Shooter on your team.

4.5 Stars
FBI Agent Gardner Camden is part of the Patterns and Recognition unit, PAR that tackles challenging cold cases, finding clues others have missed. Each quirky member is gifted in their specialty: a mathematician, a firearms expert, and a computer analyst.

Gardner’s team is called out when DNA of a murder victim matches a serial killer thought to be dead. Soon there’s another murder that seems to be connected and the team is tasked with finding the killer. It quickly becomes apparent this killer knows of the PAR unit and is leaving them clues. With the mistaken identity of the first murder, the FBI wants the case solved quickly and quietly and they want PAR to do it. They hop from scene to scene, as more is revealed, an undercurrent of urgency threaded through the narrative, keeping me on the edge of my seat!

Gardner is an interesting and likeable hero; one I rooted for! His eidetic memory and knack for connecting random details/patterns make him excellent in solving cases, but the ins-and-outs of social interactions seem to escape him. Gardner’s backstory and how he ended up on the team is revealed, but the other’s backstories are only lightly touched on. Callie, a mathematician, Shooter, a firearms expert, Frank their supervisor, and the newbie, Richie. I look forward to getting to know more about them and seeing them settle in together as a team.

Head Cases was a thrilling mystery that had me hooked from the start! I can’t wait for the next one!

I alternately read and listened to Head Cases and can recommend either version. Will Damron is a new-to-me narrator, and he performed Gardner with a kind of matter-a-fact tone, something that fit with his character’s personality perfectly! I enjoyed his performance of all voices and I hope he continues to narrate the series!

FBI Agent Gardner Camden is part of the Patterns and Recognition (PAR) unit, aka the squad of brilliant but totally unconventional agents who specialize in solving cold cases by piecing together intricate patterns in crimes. Usually, they work from the comfort of their Jacksonville office, but when DNA evidence ties a recent murder to a supposedly dead serial killer, everything changes. Gardner and his team are sent to Texas to lead the investigation. Things take a turn when another serial killer turns up dead in a different state, and the team is left wondering: Are these murders connected? And is someone out there delivering their own brand of vigilante justice? With cryptic clues leading them across the country, the pressure is on to solve the case before the killer strikes again.

I'll admit it—this one started a little slow for me, and it took a few chapters to really get into the story. BUT once the investigation began gaining momentum, I was hooked. What really made this book stand out for me was the focus on the team dynamics. The PAR team isn't your typical FBI crew—they're messy, flawed, and relatable, which made me care about their story just as much as the mystery itself. And with multiple murders and layers of deception, the plot kept me guessing all the way to the end!

This was my first John McMahon book, and now I'm definitely curious to check out more of his work. If you're into crime stories with unique characters, complex investigations, and a fresh twist on the usual FBI drama, you might want to add this one to your TBR!

Thank you to NetGalley, St. Martin's Press, and Minotaur Books for an advanced copy of this book in exchange for my honest opinion!