Betty Tregarth is forced to go with a group of men led by Bernhard Raxel. Earlier Chief Inspector Teal had told the Saint that he suspects Raxel of planning the 'crime of the century', having killed an undercover officer planted by Teal for more details. Betty works at a research plant perfecting nerve gas and Raxel has kidnapped her brother as security for her cooperation. He wants to employ nerve gas in a robbery to steal the plates and paper from the Bank of England's printing house. Teal intercepts one of the safe-crackers Raxel intends to use in the raid and substitutes the Saint, who, fortunately, is able to prove his safe-breaking skills to Raxel's satisfaction. All is now in place for the crime of the century.