Untied Lines: A Mick Nassau Key West Mystery

by D.L. Mitchell

“A non-stop tale of intrigue, romance, and resilience. Mitchell masterfully intertwines a gripping mystery with themes of friendship and redemption, creating a story that's as emotionally compelling as it is suspenseful. Five Stars!” –Cam Torrens, bestselling author of the Tyler Zahn mystery suspense series

Grappling with an unplanned retirement and searching for purpose, former Special Agent Mick Nassau heads to Key West for a long-overdue break and finds himself in the path of a looming hurricane — and unexpected danger. What starts as a simple visit with his best friend, Jack, takes a dark turn when Jack is found critically injured aboard his boat under suspicious circumstances.

The accident seems random — until Mick's instincts tell him otherwise. With Jack clinging to life, Mick plunges into a shadowy world of mysterious offshore treasure dives and unsavory locals with hidden motives. As he pieces together a sinister puzzle, he uncovers connections far more dangerous than he ever expected. Joined by Jack's sister and a trusted network of old friends, Mick races against time to expose the truth and protect those he cares about.

Filled with heart-pounding action and unforgettable characters, Untied Lines delivers a high-stakes mystery that will keep you riveted until the final twist.

267 pages, Kindle Edition

Published September 11, 2025

About the author

DL Mitchell is the author of the Coral Shores Veterinary Mystery series and a 2024 Nominee for Georgia Author of the Year. Trust the Terrier won the 2024 Killer Nashville Silver Falchion award for best cozy and second runner up for best mystery.

She brings her unique perspective as a practicing small animal veterinarian to the world of mystery fiction. With experience in bustling, big-city hospitals, her transition to a house call concierge veterinary practice has enriched her storytelling with firsthand encounters and insights into the human-animal bond.

She loves spending time with her husband, daughter, and their menagerie of pets, planning the next travel adventure, and running nearby trails. She’s a scuba diver but gets seasick, and when she’s on the road, she travels with her espresso machine and her blow-up, stand up paddle board. ​

Actively engaged in the Atlanta Chapter of Sisters in Crime and the Atlanta Writers Club, DL Mitchell finds support and camaraderie within this creative community

Reviews

[Gwen Chester · Rating 5 out of 5]

This book is fantastic and I enjoyed reading right from page one until the end.
The book has so many things going on that it keeps you right on the edge of your seat and wanting to know what happens next. If you are looking for a good book that has romance, suspense, mystery and more you have found your book in "United Lines". I really enjoyed reading the book and I know you will too. Let us know what you think. I highly recommend this book to you all.

Here we have a story of a Special Agent Mick Nassau that had just lost his job so he went to visit one of his best friends, Jack in Key West for a long over-due break. And now Mick is right in the path of a hurricane. So now he and Jack are running around the area trying to help everyone get ready for the hurricane. Jack sends Mick back to his house while he does one more check on his boat. Jack never returns from his boat so after the worst is over Mick and Bea, Jack's girlfriend, go out to search for him. They find him critically injured aboard his boat under suspicious circumstances. From there the chase is on. Who tried to kill Jack? Is there any evidence that Mick is overlooking? Will Jack ever get his memory back? I guess we should be thinking will Jack be okay? He has a severe concussion and is still unconscious. And then he is having emergency surgery for a brain bleed. The whole town is praying for his recovery.

[Shree G · Rating 5 out of 5]

Untied Lines is a fast-paced mystery set in the Key West area. The protagonist, Mick Nassau, is an ex-Navy investigator whose reunion with his best friend Jack turns into a frantic whirlpool of circumstances that leaves Mick and other characters on a high-stakes mission to uncover the truth.

In the same class of storytelling as John Grisham and Michael Connelly, this debut thriller by DL Mitchell was truly an enjoyable read. Scenes of locales from the book often reminded me of the settings in John Grisham's recent Camino Island trilogy, and it's also probably why I enjoyed reading the book so much. The aftermath of the hurricane is also something I immediately related to the Grisham trilogy, and the yacht. Who doesn't love stories about life on a yacht?! However, the plot in both books are totally different. The common element between both authors is that both keep the reader guessing about what might happen next, and the plot is engaging to say the least.

Thanks to the author infusing real restaurant and place names into the story, it was easier to assimilate the scenes in the book by looking up those places on Google Maps and drooling over the menu! I literally walked alongside Mick using Google Street Maps when he took a right on Elizabeth St. to walk into the Conch Republic Seafood Company restaurant.

I thank DL Mitchell, Book Sirens, and Black Rose Writing for sending me this fabulous thriller as an ARC. I can't wait to read other readers' reviews and look forward to the author's next thrilling book!

[Dawn · Rating 5 out of 5]

engaging & entertaining

A twist on the DL Mitchell I’ve come to know thru her Coral Shores Veterinary Mysteries, this takes things up a notch with a suspenseful and dangerous investigation that weaves us thru the streets of Key West and Miami hunting dangerous criminals and lost treasure. A touch of romance & a cute pup thrown in & we’ve got a new hero - ex FDLE special agent Mick Nassau - to hopefully see more of in the future.

[Linda Foster · Rating 5 out of 5]

This was an interesting and enjoyable read; an intriguing mystery full of suspense and entertaining characters. Ex-Special Agent Mick Nassau is a likeable individual, and his best friend Jack is well-liked in Key West. What happens is no accident and Mick decides to investigate. The events that enfold lead to more danger and the offshore treasure dive scene of corruption. The story is fast-pasted and riveting. A great ending. I am hoping that there’s a series coming from this book with Mick Nassau in his new role.
Highly recommend.

[Becca · Rating 5 out of 5]

What a book! I loved it. Good action, great mystery, great characters. An all around perfect whodunnit. I had a duh moment at one point because I kept reading the title as United instead of United so I was confused for a bit🤣🤣oops. I know Frank & Bryce have careers of their own, but I'm hoping to see a lot more of them with Mick. They all make a great team. I look forward to the next books!

[Trudy Boyd · Rating 5 out of 5]

so glad the way you ended this!

So many things happened in this book and you didn’t leave us hanging. You gave every situation closure. Even for Bob, and to me that was the best! I hope there will be a second book and it will become a series!

[Jacqueline · Rating 5 out of 5]

I am an ARC reader for Book Sirens and this is my honest opinion. I read this book in one day - it's a very entertaining story with lots of elements that make me hope that as a series it's going to carry on as well as it started. I am a little bit hooked on stories set in marina communities in Florida - in this case, Key West. The author, like others I've read who set their stories in similar places, describes a community where friends are good, lifelong friends, always there for each other, the food, especially locally caught fish is delicious, as is the Key Lime pie and being out on a boat is wonderful. The principal character of this story is a government special agent, "retired" due to an incident, who goes to Key West to spend time with his old Navy friend. The story that unfolds finds Mick investigating an attack that turns out to have far reaching implications, and changing Mick's life forever. A rescue dog named Bob is involved, making this a potential ongoing favourite

[Christmas Angel · Rating 5 out of 5]

Such a wonderful story with relatable characters and a charming BOB to round out the picture. Couldn't be more perfect. Highly Recommended.

[Lori Peterson · Rating 5 out of 5]

Received as a review copy from Booksirens, this is an honest review. United Lines is a beauty of a read and makes it a great book to enjoy if anyone is looking for an addictive beach read.

Immersive with its colorful environment of the Florida Keys and well anchored with characters as a wild thrill ride of mystery finds former special agent Mick Nassau gets thrown into after the devastating hurricane. After discovering his best friend Jack has assaulted, Mick cannot ignore that what happened could ever be accident. As Mick and his friends investigate in secret, the closer they get to the truth pushes those behind Jack's initial assault to act even more to keep themselves off the radar. But Mick Nassau isn't done hunting and so whatever it takes for justice for anyone.

Highly recommended.

[Sharon · Rating 5 out of 5]

Thank you to Book Sirens and author DL Mitchell for the opportunity to review an advance copy of Untied Lines. It was a very enjoyable read.
D.L. Mitchell has a talent for creating characters I'd love to be friends with. I could see myself lounging on the deck of Bravo Zulu, cruising around the Gulf, drinking beer with the gang, and watching the glorious sunset.
The story is told in third person from the POV of Mick Nassau, who has been forced into retirement from his investigative special agent position with the Florida Department of Law Enforcement in Tallahassee. At loose ends, Mick comes to Key West to visit Jack, his best friend from the Navy, who is living the dream running fishing charters. Shortly after Mick arrives, the town prepares for an impending hurricane, but since it's only expected to be a Cat 1, no one is evacuating.
Mick stays at Jack's house while Jack goes to the marina to secure his boat and check on some friends. Afterward, he plans to spend the night with his girlfriend, Bea, at her house. So Mick doesn't worry when Jack doesn't come home while he weathers the storm alone. But the next morning, a frantic Bea knocks on the door. Jack never showed up at her place the night before.
When they go to the marina, Jack's truck is still there, and Jack is lying on the floor of his boat, unconscious and badly injured. At first, they assume he suffered an accident caused by the hurricane, but on closer inspection of the clues, Mick realizes Jack was attacked and is determined to get justice for his friend.
It's a murder mystery, so I assumed Jack would die. But Jack pulls through, and as a reader who liked this character, I was glad. Conveniently for the plot, Jack doesn't regain his memory of the event until much later. There is a murder a little later in the story, but it's someone who needed killing.
There's also a little romance, as Mick gets closer to Jack's sister, Jo, a veterinarian. And she's caring for Bob, an adorable mixed-breed dog who needs a home.
The author did a great job describing the Key West setting: the scenery, the food, the ambience. I'm ready to pack my bags and move there.

[Shilo Goodson · Rating 4 out of 5]

This was an enjoyable book. It has a 5-star plot. While I had some of the information figured out early on, there were still a few surprises along the way. I like that the setting was so well-described that I could imagine myself there. Plus, there's an adorable dog, and that just really adds to the story.

There are two main reasons why this book got 4 stars rather than 5. First, I felt like some of the dialogue felt a bit choppy, especially toward the beginning of the book. Second, there is a touch of romance, but I never really get a feel for why they like each other. Suddenly, our main character is thinking that he might like this woman, but before that, there were no physical indicators of these feelings or anything said that indicated that there was anything romantic between them.

This book does have some swearing. While I wouldn't consider anything graphic sexual content, there was at least one scene where it started heading down the "I'm feeling uncomfortable as a reader" direction. Take into account that I like clean/cozy romance/mysteries. If you like your romance a little spicier, the scene likely won't bother you. When it comes to violence, there are several murders and attempted murders, but they never get graphic.

Overall, I enjoyed this book. It looks like it's planned as the beginning of a series. I would read the other books in the series. I would love more background on Mick in future books.

I got a free ARC from BookSirens, and I left a voluntary review.

[James Foley · Rating 5 out of 5]

"Untied Lines" is a compelling mystery that artfully blends the laid-back, vibrant atmosphere of Key West with a gripping narrative that keeps readers guessing. The novel introduces us to Mick Nassau, a special investigator for the Florida Department of Law Enforcement who has been unceremoniously pushed out of his job by the governor. Seeking solace and possibly some direction, Mick heads to the balmy shores of Key West to visit his old friend, Jack.

The idyllic escape takes a dark turn when Jack is found clinging to life on his boat as the result of a traumatic head injury. What begins as a spontaneous visit quickly spirals into a deeper investigation, as Mick's instincts kick into high gear and he finds himself propelled into a complex web of intrigue. "Untied Lines" distinguishes itself not just as a mystery but also as a rich exploration of friendship, loyalty and the lengths one will go to protect those they care about.

DL Mitchell's love letter to Key West, its sun-soaked streets, eccentric locals, and the lure of the ocean creates a beautiful backdrop that enriches the narrative and provides readers with a sensory experience that complements the unfolding mystery. A must-read for fans of the genre and anyone looking for an exciting escape. Highly recommended.

[Christine Choptovy · Rating 5 out of 5]

An awesome mystery/thriller. Mick Nassau has found himself at major crossroads in his life. He was working for Florida law enforcement but was forced into early retirement because he refused to abide by office politics. His friend Jack invites him to come spend time in Key West. Jack owns a as cottage and a charter yacht. Mick arrives hours before a hurricane is set to make landfall. Mick takes shelter at the cottage and Jack decides to stay with his boat. After the storm is over, Jack’s fiancée finds him brutally injured. Mick is certain that Jack was injured by an unknown assailant not by injuries caused by the hurricane. Jack didn’t tie down all of the boats lines (hence the title) and Mick knows that Jack takes meticulous care of the boat. Matters continue to devolve. Will Jack recover from his injuries. What did Jack witness that he was so seriously injured? Can Mick get to the bottom of what’s happening? You’ll need to read the book to find out! I guarantee you won’t be disappointed and I can’t wait to read the next book in the series.

I received an ARC of the book and this is my personal opinion.

[Gary Gerlacher · Rating 5 out of 5]

Recently retired Mick Nassau is looking for some quiet relaxation and travels to Key West to spend time with his good friend Jack Barton. Those plans are disrupted by the arrival of a hurricane, and a serious injury to Jack that requires him to be airlifted to Miami. Everyone attributes the injury to a tragic mishap during the storm, but Mick is convinced it was no accident.

Untied Lines follows Mick as he investigates the injury to his friend, and is soon drawn into a larger conspiracy. Mitchell drops the reader in the middle of the tight knit community of Key West, and surrounds you with the local traditions and landmarks as the story evolves. The characters are as rich and diverse as the Key West culture, and the story builds effortlessly to a surprise ending. Kick off your shoes, curl up in a hammock, and enjoy every minute of this cozy mystery.

[Lauryn Gilliam · Rating 5 out of 5]

“Untied Lines” is one of those great books that grabs you from the start and stays with you long after you finish. Mick Nassau, a detective recently retired from the Miami Police Department, heads to Key West to rebuild his life, only to be thrown into chaos when a dear friend is mysteriously injured during a hurricane. The mystery of what happened and who did it, pulls him back into investigation mode, even as he tries to piece together his own sense of purpose. Mitchell weaves suspense with soul in such a natural way—you feel the grit of a storm, the warmth of friendship, and yes, even the taste of Key lime pie along the way. With vivid Key West sunsets as a backdrop and genuinely moving storytelling, this novel is equal parts mystery, resilience, and heart. I felt like I was there and I can't wait for the next t Mick Nassau adventure!

[Travis Tougaw · Rating 5 out of 5]

A storm is brewing…grab Untied Lines and hunker down! Mick Nassau needs a change of scenery. Forced into retirement from his job at the Florida Department of Law Enforcement, he visits his friend Jack in Key West. What’s supposed to be a relaxing trip sees Mick back in an investigator’s role when Jack is mysteriously injured during a hurricane. With the help of friends new and old, Mick digs into the case and refuses to let go until he gets to the bottom of it.

D.L. Mitchell’s Untied Lines is a fast-paced read sure to please any mystery lover. Fascinating characters and well-chosen details make the setting come to life. The tightly constructed plot and pacing showcase Mitchell’s skill as a writer of whodunnits. I highly recommend this book!

[Bonny Beswick · Rating 4 out of 5]

I read a pre-release copy of the book courtesy of LibraryThing.
Untied Lines opens with an awesome first line, encouraging me to keep going. It was a good read, easy-to-follow plot and well edited.
There was a wonderful sense of place in Key West and the Keys. If you've been there, you walk down the streets with the characters. If you haven't, the descriptions make you want to rub elbows with the Conch's, especially when it comes to the food!
I loved the inclusion of Bob the Dog!
The story line is straight forward, with a somewhat predictable ending, which is nice to have in these unsettled times.

[Shelly Neinast · Rating 5 out of 5]

A rare friendship

I really enjoyed reading this book. It was a lot different crime detective story than I have ever read. The characters were interesting and enjoyable to read about and I loved how the protagonist was so involved and determined to help his best friend to solve his attack or injury.

You don't find that kind of friendship anymore.

The storyline was great and informative and carried through to the end. The pace was nice and I loved how the author described every scene in detail and made me want to visit Key West.

I would love to read more from this author.

I received an advance review copy for free, and I am leaving this review voluntarily.

[R B · Rating 5 out of 5]

A thoroughly enjoyable read. Mick Nassau is a relatable character, searching to rest and recharge from a career in law enforcement until his best friend is attacked and he finds himself thrown into an investigation. Mitchell expertly uses the perfect setting of Key West to add to the atmosphere and intrigue of the story. Untied Lines has something for everyone - friendship, suspense, romance and redemption - all in a well crafted story that will keep you on the edge of your seat. Well done! Can't wait for the next book in the series.

[Sharon · Rating 4 out of 5]

“Untied Lines” is an advertisement for Key West, its food and nightlife scene. There is some suspense at the beginning and about halfway through, but the location kind of overshadows the plot. Mick, the main character, is visiting his friend Jack and trying to figure out the next phase of his life. The book is well written and I liked the characters of Mick, Bryce, Frank, Jo and Bea. Would have like more background on the salvage diver and Moreno. Good summer read. I received an advance review copy for free from BookSirens and am leaving this review voluntarily.

[Jennifer · Rating 2 out of 5]

Thank you LibraryThing for the advance copy. I was really disappointed with this. Based on the description: "Filled with heart-pounding action and unforgettable characters, Untied Lines delivers a high-stakes mystery that will keep you riveted until the final twist" and the cover, I was expecting a suspenseful thriller. I guess this is what people call 'cozy' and I'm not a fan. It was really repetitive too. I would say 80% was spent talking about food, 15% discussing the hospital, 4% working on the mystery, and 1% romance.

[Vicki · Rating 2 out of 5]

I received an arc from netgalley.

It only took me a few hours to read however it was a very slow paced read and I didn't feel like I connected with the characters.

It told a nice story and I could tell the author had done a lot of research before writing about the places she covered in the book.

I loved the parts about bob the dog and the romance story with some of the characters where nice however I was expecting more of a thriller and the twists it promised fell flat for me.

Thank you for letting me read and review.

[Cam Torrens · Rating 5 out of 5]

DL Mitchell delivers a non-stop tale of intrigue, romance, and resilience. Set against the dramatic backdrop of a Key West hurricane, her novel “Untied Lines” follows former investigator Mick Nassau as he delves into his best friend’s suspicious injury while navigating new relationships and personal challenges from a forced retirement. Mitchell masterfully intertwines a gripping mystery with themes of friendship and redemption, creating a story that's as emotionally compelling as it is suspenseful. Five Stars!

[Glitter · Rating 3 out of 5]

Thank you for letting me read your book! I think that a second book might clear up the first. The beginning was fantastic and moved quickly, I truly enjoyed the book until the MAJOR EVENT! Then I felt like the only thing I connected with was the food references. The book picks up again at the end, reengaging me. It is well written which makes a huge difference in my perspective. I’m going for a second!

[Niamh McAnally · Rating 5 out of 5]

Mystery, Murder and Mayhem on the wonderful island of Key West, Florida. Mick Nassau is not just a former special agent but a loyal friend, who puts his own recent troubles aside to help a fellow veteran. A well written, easy to read novel, filled with colorful descriptions of the Florida Keys, an array of interesting characters, and a burgeoning romance. The story zips along to a satisfying conclusion and leaves you waiting for the next installment of Mick Nassau. Highly Recommend!

[Reader · Rating 5 out of 5]

A GREAT new read by DL Mitchell. "Who in their right mind ventures into the eye of a hurricane?". From the first line through to the end, Mitchell provides a gripping pace and brilliantly written tale of mystery, suspense and friendship via a fantastic cast of characters. I hope this is not the last we hear from former Special Agent Mick Nassau! Five Stars!

[KerryO · Rating 5 out of 5]

I loved Untied Lines which takes place in a favorite location, Key West, featuring Mick Nassau as protagonist. This story involves salvage diving for treasure, another fav, with a wonderful cast of likeable and well-developed supporting characters. I can only hope that is the first of Mick’s adventures. I received an ARC from Book Sirens and the opinions expressed are my own.

[Barbara Tobey · Rating 5 out of 5]

An engaging and enjoyable romantic suspense. Love the location of Key West. Many great characters, including Bob the dog. I look forward to reading more by this author. Thanks to the publisher for providing a copy via NetGalley. My review is voluntary.

[jamie Wyatt · Rating 5 out of 5]

I’m giving this book 5 stars why because it’s a good read with a little bit of everything so captivating and exciting to read with awesome characters it’s got suspense and mystery with Romance and lots of details about the key west! Read it you will want more!