The film's early scenes introduce us to the eight characters we follow - each are fictional but all are played by real firemen. One 24-hour period is dramatised. In the morning, the men leave their homes and ordinary occupations to start their tour of duty. A new recruit arrives and is shown the ropes. There is a full moon due and warning comes that a heavy attack is anticipated.
Night falls and the sirens begin to wail.
The unit is called out to a riverside warehouse where fire threatens an ammunition ship at anchor by the wharf. The fire is fought and finally mastered, though one man is lost and others are injured. The ship finally sails with the morning tide. The way the story is structured provides a portrait of what was then a beseiged Britain that is astonishingly intimate. One Man Went To Mow and other popular songs of the day.