Cass Lynch has achieved the post of third officer aboard her beloved Norwegian sail-training ship, Sorlandet. They're sailing from Norway to Ireland as part of the Tall Ship's race. An unnerving early-morning encounter leads to suspicions that there's a stowaway aboard - yet a police search finds nobody.

Then one of the trainees goes missing ... Cass and her lover DI Gavin Macrae find themselves up against a ruthless killer. Cass also needs to confront her personal dilemma: if she wants a settled life with Gavin, she'll have to leave the sea, but could she bear to do that?