A London cabby uncovers the city's secret nightlife in a surprising plug for postwar National Savings.

When a disgruntled passenger complains to a London cabby that the postwar nighttime capital is as "dead as mutton", the gauntlet is thrown. Hidden behind the dimly-lit city streets, a bustling world of nocturnal activity is revealed: Fleet Street printers, courting couples waiting for the last train home, bleary-eyed MPs after a late-night sitting, and the Post Office underground railway distributing the next day's mail.

An all-night taxi-driver shows a passenger London's night activities: a newspaper printing press; a Post Office sorting office and the underground postal railway, King's Cross railway station; Covent Garden, and MP's leaving Parliament after an all-night sitting.