August 1920, Dublin, Ireland: A fraught task keeps Verity and her husband Sidney in the country after their initial clandestine mission has been completed: the traitor Lord Ardmore is scheming to employ the deadly phosgene gas he's stolen for some terrifying purpose, and the couple will need both the Crown forces and the rebels' help to thwart him.

As they pursue their quarry, they are drawn into a case involving a series of cunning and brazen jewel thefts. Many believe it is the work of the Irish rebels, seeking to fund their revolution, but when Verity and Sidney are also approached by Michael Collins and the Irish Republican Army to unmask the thief, they suspect he may instead be an opportunist using the political unrest as a cover for his crimes.

As the thief continues to pull ever more risky jobs—including targeting Verity and their friends—the couple receive new intelligence that the gas they seek may be intended for a crowded event, one that the entire world will be attuned to. They must stop Lord Ardmore at all costs—or the consequences will be devastating . . .