Laurence and Temeraire arrive back in the United Kingdom, following their evacuation of Danzig in "Black Powder War". Their relief at arriving safely is short-lived as Napoleon continues his preparations for an invasion of the British Isles. When questioned about the lack of British air support for the Prussians, Laurence discovers that Britain had no dragons to spare: a flu-like epidemic has infected the greater part of them, and British science has yet to devise a cure. To combat it, Temeraire, Iskierka and the ferals are forced to fly frantic patrols, both as a show of force and to prevent Napoleon from getting reconnaissance in over the contaminated coverts; at one point Temeraire is forced to knock a French courier-dragon, Sauvignon, out of the sky and down into one of the coverts, risking infection himself.