Lady Arianna, now the Countess of Saybrook, is settling into married life with her new husband. To celebrate his birthday, she finds the perfect gift: a rare volume of botanical engravings on Theobroma cacao - or chocolate - in an exclusive bookshop. But she is forced to fight off a stranger who tries to steal it way from her.

Arianna forgets about the strange incident - until she and her husband attend an important government party on a country estate, where her assailant reappears and turns out to be a Russian diplomat. Events grow more ominous when Arianna discovers sensitive government documents hidden in the book's binding - documents that suggest someone she and Saybrook hold dear is a traitor to King and country.

Murder. Treason. Money. Power. Once again, Arianna and Saybrook are drawn into a shadowy world of international intrigue. To unmask the real villain, they journey to the Peace Congress in Vienna, where amid the seductive pomp and pageantry of Europe's royalty, they must root out a cunning conspiracy - armed only with their wits and their expertise in chocolate....