With the outbreak of the Second World War, the Saint has almost turned respectable.
Employed by a secret wing of the government to track down spies and take on cases the ordinary police can't touch, he is dining in Washington DC when a young woman asks for his help.
Her father, a noted scientist, has invented a new form of synthetic rubber - and now he has disappeared, and she is under threat.
Simon is sceptical - but he swiftly realises there's something to her story.
Soon he finds himself on the hunt of a band of conspirators who will stop at nothing to ensure the invention never sees the light of day.