In Black Powder War, Captain William Laurence and Temeraire - along with the surviving members of their crew - are ordered to make all haste and return from the mission to China via Istanbul, where they are to take custody of three dragon eggs purchased from the Ottoman Empire by the British Government.

Deciding to eschew the Allegiance, which suffers fire damage at the opening of the novel, Laurence takes the services of a guide named Tharkay, the well-bred but ostracized child of a British diplomat and a Nepalese woman.

Once there, however, they face clear betrayal; the Sultan has chosen to ally himself with Napoleon, probably at the urging of Lien, who is now present in his court, and has seized the exorbitant payment offered him by the British Crown whilst simultaneously reneging on any intent to hand over the eggs in return.

The only good news to emerge from that battle is a Prussian declaration of alliance against Napoleon for what history today calls the War of the Fourth Coalition, and Laurence routes his travel through that nation.

Despite the personal presence of King Frederick William III of Prussia and his wife Queen Louise, the Prussians are soundly defeated in the Battle of Jena-Auerstedt, and Temeraire is forced to ferry the royal family away.

Using these dragons and techniques observed in China, Laurence is able to rig out the entire flock as public transportation and evacuate the city, dropping the civilians into the waiting arms of the Royal Navy.