Morale is flagging and standards have slipped aboard HMS Suffolk. New Captain Martin Brooke finds himself thrown in at the deep end; he and his fractious crew are fast approaching Operational Sea Training, the toughest test of their careers, and time is running out.

Unfortunately, things don't run as planned on Martin's first day at sea. Suffolk becomes embroiled in the frantic rescue of a trawler full of illegal immigrants stranded in the busy shipping lanes.

Personal lives aboard ship run amok. Second in command, Jenny Howard faces a crisis when her boyfriend asks her to move to New York just when Martin needs her most; engineer Andy is shocked to discover that his protégé Dave is the father of his daughter's new born baby, and a run on shore goes horribly wrong for ratings Mickey and Scouse.