The service of Britannia is not for the faint of heart—or conscience...

Emma Bannon, Sorceress Prime in service to Queen Victrix, has a mission: to find the doctor who has created a powerful new weapon. Her friend, the mentath Archibald Clare, is only too happy to help. It will distract him from pursuing his nemesis, and besides, Clare is not as young as he used to be. A spot of Miss Bannon's excellent hospitality and her diverting company may be just what he needs.

Unfortunately, their quarry is a fanatic, and his poisonous discovery is just as dangerous to Britannia as to Her enemies. Now a single man has set Londinium ablaze, and Clare finds himself in the middle of distressing excitement, racing against time and theory to find a cure. Miss Bannon, of course, has troubles of her own, for the Queen's Consort Alberich is ill, and Her Majesty unhappy with Bannon's loyal service. And there is still no reliable way to find a hansom when one needs it most...