July 1912. Lady Hardcastle and her tenacious lady's maid, Florence Armstrong, are enjoying a convivial gathering at the home of their dear friends, the Farley-Strouds. The only fly in the idyllic ointment seems to be the lack of musical entertainment for the forthcoming summer party--until, that is, Lady Hardcastle's brother Harry calls with news of a murder.

Harry dispatches them to Bristol on behalf of the Secret Service Bureau, with instructions to prevent the local police from uncovering too much about the victim. It seems an intriguing mystery--all the more so when they find a connection between the killer and an impending visit from an Austrian trade delegation, set to feature a very important guest...

Summoned to London to help with some very important security arrangements, the intrepid duo will have to navigate sceptical bureaucrats, Cockney gangsters and shadowy men in distinctive hats in their attempts to foil an explosive--and internationally significant--threat.