Neither Inspector Teal nor the Saint are impressed by Peter Corrio, a smug private detective who boasts to them that his security system for the fabulous Oppenheim emerald is fool-proof. They are suspicious that he has managed to solve so many jewel thefts that have evaded the police. Then the Saint meets Janice Dixon, who tells him that her brother was killed trying to escape from the police having had jewels planted on him by Corrio. She believes that Corrio himself has engineered the recent thefts in order to return the jewels for the rewards involved. Then Janice is snatched and taken to a boat owned by Corrio. Not only is the Saint going to find her, he plans also to steal the emerald and show Corrio which of them is the smarter detective.