Death on a Shetland Isle — Marsali Taylor

Readying her Norwegian sail-training ship, Sorlandet, for a fresh voyage through the Shetland Islands, Cass Lynch has the shock of her life when the new third officer is a ghost from her past - the man she thought she'd left to drown in the Atlantic eleven years before.
Cass has an odd feeling about some of the new trainees: a slick city-boy, and a brother and sister. As her distrust of the newcomers deepens, two people go missing and a third is found dead. Struggling to confront the ghosts of her past, the deceased of her present, and the man of her future, Cass must out-manoeuvre the killer before she too becomes one of the victims.