Professor Willingdon (Barry Jones) – a timid but crazed English nuclear scientist – runs away from a government research centre with a stolen UR-12 atomic bomb in his valise.
In a letter sent to the British Prime Minister (Ronald Adam), he threatens to blow up central London if the Government don’t announce the end of the production of all nuclear weapons within seven days.
The government has no intention of capitulating to Willingdon’s ultimatum, and special agents from Scotland Yard – led by Superintendent Folland (André Morell). Meanwhile, most of London is evacuated.
The middle-aged Piccadilly street-walker Goldie (Olive Sloane) takes Willingdon into her flat (for what she can get out of him), not realising who he is.
The film has a blunt message, subtly told within the folds of a spine-tingling story.
Other cast members included Joss Ackland, Rupert Davies, Sam Kydd, Patrick Macnee and Henry McGee. Newscasters Frederick Allen, John Snagge and Merrill Mueller appeared as themselves.