Lacey Flint has left her former position as detective on the Major Investigations Team and her boss, Detective Inspector Dana Tulloch, for the calmer waters of London’s Thames Marine Unit in Wapping, content to monitor the river and scale back opportunities for the physical and emotional trauma suffered on her most recent cases. Living on a small but beautifully crafted houseboat in the riverboat community on nearby tributary Deptford Creek, Lacey’s new digs afford her the security and privacy she covet—and allow her to secretly (and illegally) swim the Thames with Ray, her neighbor and Marine Unit boss. It’s a tightly knit group, offering plentiful opportunities to watch over others while avoiding life-threatening situations.
But this is Lacey Flint, a young woman who seems to attract trouble like a magnet, as well as the romantic interest of Mark Joesbury, a detective with the Special Crimes Directorate currently on an undercover assignment. Lacey has very reluctantly admitted to an attachment to the persistent Joesbury, who has supported her in the most dangerous assignments. Mark is not about to let Lacey out of his sight or his life. Meanwhile Detective Inspector Dana Tulloch has decided to take the plunge with her partner and become a mother, a seemingly irrelevant situation that becomes unexpectedly relevant, converging with an unfolding murder investigation. The mystery takes shape when Lacey discovers the corpse of a young woman while swimming in the Thames, the body wrapped in a linen shroud. Without identification, all that can be ascertained is that the woman is of Middle-Eastern heritage, possibly from Afghanistan or somewhere similar. Suddenly, Flint is back in contact with her former squad, more bodies buried in the Thames as though they have been waiting just for her.
Lacey can’t help but assume she is meant to find the source of the bodies, trolling the river on patrol in search of unusual activity, the banks of the Thames rife with long-abandoned buildings, waterways that fill with the tide then empty, revealing those unfortunates who have found death in the water. These young women have no identities, save one possible connection to a young woman Lacey saved from drowning months ago. Beyond the presence of the bizarre shrouded bodies, Lacey is certain she is being watched, has been visited in secret by someone who leaves toy wooden boats behind in her houseboat.
In a riverside community that revels in the telling of mermaid myths and mysteries hidden in the depths, it is tempting to believe that Lacey’s visitor is a mermaid, but she is doubtful, unsettled that she hasn’t heard her nocturnal visitor nor understood the message of the toy boats. Patrolling the Thames, Lacey makes the acquaintance of an eccentric brother and sister—she an herbalist, he a physician—their riverside home filled with wild blooms for mixing healing concoctions. Exploring the watery channels in search of the location of the nameless young women, Lacey is drawn deeper into the mystery, missing Joesbury and recently worried that her security on the houseboat is but an illusion as threat draws nearer. Caught in the web of an elaborate plan, Lacey is the focus of a killer to would add her to the collection of the dead.
Intrigued, terrified and determined to find where these victims have been kept, Lacey enters a subterranean world where a killer lurks, depending on instinct and her wits to survive what appears a monster rising from the deep to claim her and the helpless young woman she is trying to save from certain drowning. Her team too far away to make a difference, Lacey is in a fight for her life against a foe she has yet to name. Discovering secrets as deep as the river currents and mired in myth, Lacey claims a place she can call home—and the freedom to follow her heart.