After James Wentworth resigned his commission in the RN he had always declined to attend the Annual Summer Ball at Fort Blockhouse, home of the navy's submarine service, but this year he decides to go. Finding he has little in common with most of the other guests he wanders out to the jetty and boards the submarine he last served in.
He joins the captain and shares a bottle with him. They were midshipmen together in the cruiser HMS Pelorus in the Mediterranean in the dark days of 1941. As they talk the story unfolds.