What a gripping and intelligently crafted read! I was completely drawn in by the dark, clever layers of this atmospheric crime thriller—full of sharp twists and an irresistible game of cat and mouse.

This FBI procedural stands out with its meticulous plotting, unforgettable cast of eccentric, offbeat characters, and a remarkably compelling lead.

A stellar series debut—I’m already eager to see where the PAR Unit heads next. With a television adaptation in the works, I can’t wait to watch this brilliant story come to life on screen.

Excellent characterization, but the plot was a bit over the top.



Review copy provided by publisher.

If you like Criminal Minds, this one will be right up your alley. Head Cases has a cool premise—a quirky team of FBI specialists solving twisted, puzzle-filled murders—and the case definitely kept me guessing. Gardner Camden is a solid lead, even if emotionally closed off, and the killer’s mind games were a highlight.

Some pacing issues and missed emotional beats kept it from being a full hit for me, but overall a strong, clever debut. I’d check out book two!

I listened to the audiobook and Will Damron is one of my favorite narrators, he did a great job like always. This one was interesting! It held my attention the whole way through and kept me wanting more. I read somewhere that this is the first of a series and I hope so! Highly recommend!

Head Cases was an excellent read. The writing was propulsive and the character development was rich. I would read more from this author.

Great first in series! A detailed crime procedural that doesn't read above your head or drown you in procedural jargon.

This is about a special group of the FBI that seems to be made up of outcasts but together form a great team. This group is brought in to hunt a killer who is killing killers. (wow thats a lot of "kills") There is your typical cat and mouse chase of the unsub and particular agent but it works.

The main agent, Gardner Camden, is a genius with zero people skills. He gives you a Sherlockish vibe, seeing things at scene that others may overlook. He thinks in puzzles and is working hard to solve this one as the fate of his unit may depend on it.

I will definitely be on the look out for book 2.

This is a solid police procedural, with interesting characters and a good mystery, I really liked the PAR unit, this has the basis for a great series featuring these agents. Pick this on cup if you enjoy a mystery with a few twists along the way that keep you guessing.

If you know me, you know I love my police procedurals and I’ve been craving a strong detective/police procedural lately. I’ve been looking for something to tie me over until the next Karin Slaughter book comes out, and I think I found a new author to watch for.

The first in a new series, Head Cases follows FBI Agent Gardner Camden and his team the Patterns and Recognition (PAR) Unit as they case a serial killer killing…serial killers. The first victim – one of Camden’s cases from years ago that the FBI thought had died. Can they catch the killer before the case become too personal?

Slow Horses meets Criminal Minds. Plenty of action and a good balance of characters. Camden has neurodivergent tendencies, and I felt that McMahon did a wonderful job of giving him growth but keeping him realistic. I primarily listened to the audiobook and Will Damron was an amazing narrator for Camden. I definitely loved the way this series started, and I can’t wait for the PAR #2. Going to have to dive into McMahon’s P.T. Marsh series next!



Head Cases is out now. Huge thank you to Minotaur Books & Macmillan Audio for my advanced copy in exchange for my honest opinion. If you liked this review, please let me know either by commenting below or by visiting my:
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Lost audio before I could finish listening. Was told they’d send a physical but that didn’t happen either so will either have to buy or never read it.

Once I really gave this book a chance, I enjoyed it! I listened to the audiobook version. Will Damron did an excellent job by bringing Gardner to life. I really enjoy quirky characters in books, and John McMahon writes them well. If you’re looking for a good police procedural thriller with a quirky main character, check this book out! Thank you NetGalley and Macmillan Audio for providing me with an ALC in exchange for an honest review.

I do not always read procedurals but as a fan of Criminal Minds like shows, I was curious about this new series. The characters were the best part of the book, their relationships with each other, their personality, their quirks. The storyline was fast-paces and interesting, kept me listening. Will be continuing the series. If you like reading about serial killers and delving into the minds of the people trying to catch them, give this a read.

Listening to the audiobook made the story even more gripping.

Thank you to NetGalley and the publisher for the ALC.

"Head Cases" is a gripping, fast-paced police procedural that hooked me right from the start. As a huge fan of Criminal Minds, I was very excited to read this book about FBI agents in the Pattern and Recognition (PAR) unit, and it did not disappoint. It was such a page-turner, and I had so much fun reading this book. The mystery was compelling, and I was fully invested. I loved the well-developed, quirky characters, and the plot twists were surprising and well-executed. I was ecstatic to learn that this will be a series, and I can't wait for Book 2!

I listened to the audiobook narrated by Will Damron. As usual, he did an amazing job bringing the story and characters to life. His top-notch narration made this an unpausable listen. He seamlessly transitioned between characters and was able to build so much tension and suspense. Highly recommend this one on audio.

Thank you to NetGalley and Macmillan Audio for the ALC in exchange for an honest review.

I listened to about 10% of the audio and couldn't really get into it, the MMC was a little "off" and I just wasn't gripped from the get-go.

Please circle back to my review for the ebook of this one but DANG!!!! This one was even more spectacular on audio.

Head Cases is my first 5 star read of 2025. This book really drew me in. I love how a group of people who hadn’t played a political game of their career were put together to form the PAR Unit. (Patterns and Recognitions Unit) They were all very intelligent and had their own strengths.

Serial killers being killed?! And little clues hidden along the way?! I felt like I could have been watching an episode of Criminal Minds. The author was able to give enough description to where I could visualize it happening, but not overkill. Now that I’m thinking back over the book, it was a clean read. It just goes to show that books don’t need romance or spice for them to be a great read. There wasn’t even a lot of cussing (which cussing doesn’t bother me, I’m married to a Marine. But it does bother some).

This book had me suspecting so many people. But I didn’t guess any of the twists. This was a quick read that I didn’t want to put down/stop listening to. But I also didn’t want it to end! I consumed most of this book by audio during my work commute. Will Damron has to be one of my favorite male narrators. He voiced Agent Gardner Camden so well. I felt like he really brought him to life. All his little quirks.

I am anxiously awaiting book 2 in this series. It probably won’t be for another year but it can’t come soon enough! I need books from each of the characters.
I think overall, I just throughly enjoyed this. I would recommend it to people who enjoy Criminal Minds or the FBI shows.

This is the first book in a new series that follows FBI Agent Gardner Camden who is in a special and new branch called the PAR Unit. This is the Patterns and Recognition unit. All the members are washed out and considered "Head Cases" as they are "freaks" and find patterns in cases to help solve... cases. Anywho, the team is brought out to a crime scene in Texas and the team starts a manhunt for a serial killer who kills serial killers. Flying all over the country trying to find the suspect by looking into old cases while the killer is taking things to a personal level for Camden. Camden is also "special" because he has an eidetic brain and can see patterns, but has a hard time in social situations so he has learned to act how other people act and think like he thinks.

This is probably one of the best books I've read this year. I don't know what it is about the MC but his struggles to connect emotionally yet understanding of himself and his willingness to try is endearing. I also love that his team and the people around him accept him for who he is. I like that this is a team full of genius misfits who get to solve terrible crimes. The humor is dry and on point and there is this juxtaposition of Camden and his partner, as she speaks modern slang and he rolls with it but is still himself. The crimes are there but it's solving the puzzle and putting all the pieces together that makes this fun. This book is worth the read, it is a crime procedural that isn't trying too hard and all of the characters have chemistry, the humor is on point and it's all together a good time. The narrator was amazing really giving the character more depth and he delivered the deadpan jokes very believably. There was only one word that bothered me at the beginning, and I don't even remember it now, but it was some medical word or body part that was pronounced incorrectly, but other than that such a great book.

Head Cases was a great first book to a possible series. I have not read books by John McMahon but I was very intrigued by the book description so I decided to give the book a shot. And it was so worth it.

Head Cases is a procedural book about outcast FBI Agents in a group called PAR (Patterns and Recognition). PAR gets its name because each member has a special gift, but most important they have the smartest minds. Despite their talents the misfit members of PAR typically are not given the best cases; generally they are only regulated to solve cold cases.

That is until recently!!!

The Director of FBI personally requests to have PAR investigate a new series of serial killings. The serial killer is hunting serial killers!!! This team was selected because of their ability look at problems from a different perpective. With this request Gardner Camden is given the opportunity to lead the PAR group to solve this case.

As the case moves forward, the killer leaves clues for the team to find. But the battle between minds of the PAR group and the killer makes it personal. Will Gardner be able to solve this killing spree with the help of his team? Will the killing spree continue? Will this case go too far and get too close to home for Gardner? All will come to a head - who will survive?

This was such a great fun first book. I really enjoyed. I felt like I was actually a part of the team with their investigation and how well it was explained, The pacing was exciting and I often felt on the edge of my seat. I highly recommend this book and really hope the author makes this a series. I will be looking for more books by John McMahon.

Thanks NetGalley and the publishers for allowing me to read this ARC book.

This book was AWESOME.

It reads like true crime, but isn’t. Following an FBI unit hunting a killer who targets serial killers…with plenty of near-misses and tricky evidence along the way. I was very invested in the characters and how the storyline would play out, and I absolutely loved that the unit this story followed was PAR—patterns and recognition—which is tasked with connecting seemingly unconnected cases through patterns in evidence that most agents would never spot.

Overall, five stars and I hope this turns into a lengthy series!

I love the crime shows like FBI, Criminal Minds, and Mindhunter, so I knew this book was going to be right up my alley. I was not wrong. This will be a book that I go back and read again in a couple months as it held my attention from the first page and never let go.

I did not like this story. I know so many people did and raved about it but I just struggled to really get into it.