The Recommended Reading Order for the Underwater Investigation Unit
If you want to experience Sloan McPherson's growth as an investigator and follow the natural progression of her career and personal life, the best path is the publication order. The series starts with Sloan as a freelance diver with a complicated family history and follows her as she becomes the anchor of a specialized police department.
Here is the recommended reading list for the main series:
- The Girl Beneath the Sea (2020)
- Black Coral (2021)
- Sea Storm (2022)
- Sea Castle (2023)
- Dark Dive (2024)
Sloan McPherson’s Next Chapter: The Specialists Crossover Series
Once you finish the main Underwater Investigation Unit (UIU) novels, Sloan's story continues. Andrew Mayne has constructed a shared universe that brings Sloan together with three of his other iconic protagonists: computational biologist Theo Cray (from The Naturalist series), FBI agent and former illusionist Jessica Blackwood (from the Jessica Blackwood series), and former CIA operative Brad Trasker (from the Trasker series).
Known as The Specialists, this team-up series should be read directly after Dark Dive. The reading order for these crossover novels is:
- Mr. Whisper (2025)
- Imposter Syndrome (2025)
- Chaos Man (2026)
Detailed Breakdown of the UIU Series
The Girl Beneath the Sea (2020)
This is where it all begins. Sloan McPherson is a police diver in Florida with a treasure-hunting background, which often puts her at odds with traditional law enforcement. While diving in a canal, she discovers the body of a young woman. The investigation leads her into a dangerous web of local corruption, drug cartels, and hidden treasure. This book establishes Sloan's complex relationship with her family and introduces the concept of the Underwater Investigation Unit.
Black Coral (2021)
Now officially working with the UIU, Sloan is tasked with investigating a submerged van in a deep pond. Inside are the remains of teenagers who went missing decades ago. As Sloan digs deeper into the cold case, she realizes that the deaths were not an accident but the work of an active, long-term serial killer who has used Florida's vast, murky waterways to hide his crimes for generations.
Sea Storm (2022)
The stakes escalate when Sloan is called to investigate a massive cruise ship disaster. Mysterious underwater explosions have crippled the vessel, and what initially looks like an accident or an act of eco-terrorism quickly reveals itself to be a complex conspiracy involving high-level corruption and international corporate greed. Sloan must navigate both the literal dangers of the sinking ship and the political minefield of the investigation.
Sea Castle (2023)
In the fourth installment, Sloan finds herself investigating a bizarre crime scene when a body washes ashore near a beachside mansion. The victim is tied to a series of high-profile art thefts and historical mysteries. Sloan must dive into deep ocean waters and navigate the secrets of the ultra-wealthy to uncover the truth behind a string of murders that stretch far beyond Florida's shores.
Dark Dive (2024)
Sloan's past and present collide when a treasure hunter goes missing under suspicious circumstances. Drawing on her own family's history with salvage operations, Sloan dives into the black-market antiquities trade. She must uncover a massive conspiracy before she becomes the next target hidden in the ocean depths.
Understanding the Crossover Books
Sloan's integration into the wider "Mayne-verse" is a major highlight for fans. While she operates independently in her first five novels, her expertise is vital to the team formed in The Specialists. Here is how she connects with the crossover team:
- Mr. Whisper (2025): Sloan initiates the case when she discovers an amnesiac vagrant in a Florida swamp who disappeared thirty years ago. As she enlists the help of Theo Cray and Jessica Blackwood, they uncover a shared childhood trauma and a master manipulator. Brad Trasker joins from the West Coast to help link the corporate espionage angles.
- Imposter Syndrome (2025): When influencers start turning up dead in bizarre, ritualistic displays—including a YouTuber encased in a salt obelisk and a TikTok star in a Nevada lake—Jessica Blackwood brings Sloan in to help decode the aquatic and forensic elements of the killer's calling cards.
- Chaos Man (2026): The team reunites when a series of seemingly unrelated infrastructure disasters across the United States are revealed to be coordinated acts of sabotage. Sloan's diving and tactical recovery skills are tested as the team races to prevent a catastrophic collapse.
What to Know Before You Start Reading
Andrew Mayne brings a unique perspective to these novels. As a former magician and science enthusiast, he infuses Sloan's investigations with authentic diving techniques, marine biology, and forensic science. The setting of Florida itself acts as a character, with its dark canals, unpredictable weather, and hidden historical secrets providing the perfect backdrop for suspense.
While the books can be enjoyed as standalone thrillers because each mystery is resolved by the final page, reading them in order is highly recommended. The character development, particularly Sloan's evolution as a mother, detective, and teammate, builds sequentially. Furthermore, the crossover elements in The Specialists will be far more rewarding if you are already familiar with Sloan's background and skills.