In Deep by Sharon Ward
When a series of accidents befalls the staff at a Cayman Islands-based oceanographic institute, the blame falls on underwater photographer Fin Fleming, who has recently joined the institute founded by her world‑famous oceanographer mother.
The arrival of her stepfather's previously unknown children threatens to sink her mother's marriage, and Fin's ex-husband steals the wind from her career sails when he publicly claims her best work as his own. Fin's life gets even more unsettled when her estranged father shows up out of the blue, after casting her adrift more than twenty years earlier. She seems to be getting her life back on course when she meets Liam, an intriguing Australian who loves diving as much as she does.
But the tide turns when Fin realizes the lethal accidents are not coincidences—the killer is targeting her family. She can trust no one and must set a course to surface the predator's identity before her family is swept away on a wave of malevolence.