This book picks up only a couple of days after the end of Throne of Jade. From Amazon:
After their fateful adventure in China, Capt. Will Laurence of His Majesty’s Aerial Corps and his extraordinary dragon, Temeraire, are waylaid by a mysterious envoy bearing urgent new orders from Britain. Three valuable dragon eggs have been purchased from the Ottoman Empire, and Laurence and Temeraire must detour to Istanbul to escort the precious cargo back to England. Time is of the essence if the eggs are to be borne home before hatching.
Yet disaster threatens the mission at every turn–thanks to the diabolical machinations of the Chinese dragon Lien, who blames Temeraire for her master’s death and vows to ally herself with Napoleon and take vengeance.
I thought this was a trilogy; however, there’s more to come. This is the third book in the Temeraire series (ISBN 0-345-48130-5). Next book: Empire of Ivory. See also His Majesty’s Dragon and Throne of Jade.