The Shadow of the Eagle — Richard Woodman

It is 1814 and Napoleon has abdicated as Emperor of the French. King Louis XVIII is brought out of his English exile and escorted back to France by an Allied squadron commanded by the Duke of Clarence. The "Great War" is at an end and Europe prepares to celebrate the return of legitimate monarchy.
But the victorious Allies are increasingly suspicious of one another. Alexander I, the capricious Tsar of Russia, believes he is the savior of the world, while Great Britain -- whose sea power has guaranteed victory at sea and contributed to the military success of Russia, Austria, and Prussia -- remains at war with the United States of America. Out of the ashes of defeat, France's greatest survivor, Talleyrand, prepares to restore his beaten country to the forefront of European politics. Amid this upheaval, discontented Bonapartists plot to restore the eagle whose shadow still lies across the continent.
Attending King Louis, Captain Nathaniel Drinkwater is alarmed to receive secret intelligence that a new and imminent threat exists to peace.