Underwater Investigation Unit Books in Order

The Underwater Investigation Unit books drop crime fiction into Florida’s canals, shipwrecks, and sinkholes. The series stars Sloan McPherson, an archaeology student and single mother who works as a diver for law enforcement. She comes from a family of colorful treasure hunters and smugglers, and that background gives her both useful skills and a reputation that makes some colleagues uneasy.

In The Girl Beneath the Sea, Sloan is doing an off duty dive for artifacts when a freshly killed body drifts past her. Suddenly she is both a potential witness and a suspect. As she digs into the victim’s past, she finds herself caught between local police, federal agents, and a drug cartel’s hunt for lost treasure. The case forces Sloan to lean on her outlaw uncle, a legendary DEA agent, and every bit of practical water sense she has just to stay alive.

Black Coral opens with what looks like a tragic crash. A car plunges into a pond known for its alligators, and the Underwater Investigation Unit is called to recover the body. While working around a curious giant gator, Sloan discovers a second vehicle on the bottom: a van containing four teenagers who disappeared thirty years earlier after a rock concert. Officials lean toward accident. Sloan’s instincts and additional evidence point to a serial killer whose work may stretch across Florida.

In Sea Storm, a distress call pulls Sloan and her partner Scott Hughes out to a cruise ship off Fort Lauderdale that is sinking after a mysterious explosion. They race to evacuate passengers and crew while fire tears through the decks. Initial theory blames ecoterrorists, and the FBI quickly asserts control, but none of the available facts quite line up. As a tropical storm moves in and evidence threatens to wash away, Sloan keeps following the parts of the case others would rather ignore and uncovers a motive that has more to do with money and power than ideology.

Sea Castle finds the Unit politically sidelined, with Sloan temporarily reassigned. A naked young woman washes up on a Fort Lauderdale beach with a rope around her neck. The medical examiner rules strangulation by hand, not by the apparent ligature, and the victim’s pristine condition does not match the time she supposedly spent in shark infested water. Sloan’s gut says murder, not suicide. To push the case forward she partners with Gwen Wylder, a brilliant but abrasive homicide detective, and starts connecting the dead woman to a pattern of disappearances and deaths along the coast that suggest a charismatic predator hiding behind different identities.

In Dark Dive, public pressure brings the disbanded Unit back. Sloan’s first new case is personal: family friend Fred Stafford has vanished, leaving his truck near an unmarked sinkhole. As she and Scott dig, they find gambling debts, a connection to a loose crew of cavern obsessed divers called the Dive Rats, and something in Stafford’s storage shed that suggests he was involved in more than harmless treasure hunting. The search pulls Sloan into a collision of a long buried Florida cold case, local legends, and a conspiracy that reaches further than she expected, all while forcing her to confront fresh trauma from a near fatal underwater accident.

Taken together, the Underwater Investigation Unit novels read like a mashup of police procedural, adventure story, and Florida noir. The water is always beautiful and always dangerous, and Sloan’s willingness to dive where others will not keeps uncovering crimes that were meant to stay sunk.