"When a bomb destroys the recently formed Special Irish Branch of Scotland Yard, all fingers point to the increasingly brazen factions of Irish dissidents seeking liberation from English rule. Volunteering their services to the British government, Barker and Llewelyn set out to infiltrate a secret cell of the Irish Republican Brotherhood known as the Invisibles. Posing as a reclusive German bomb maker and his anarchist apprentice, they are recruited for the group's ultimate plan: to bring London to its knees and end the monarchy forever."