Sebastian and Hero travel to Paris in March 1815 to find his long-missing mother, Sophie, only for Sebastian to discover her dying near the Île de la Cité. She had been living under an assumed name with a former Napoleonic marshal now serving the restored Bourbon government and the negotiations reshaping Europe.
French officials want the notorious Englishwoman's death forgotten, so Sebastian traces her secret life himself. As Napoleon escapes Elba and Louis XVIII's regime begins to collapse, the murder exposes divided loyalties, Jacobite history and information that could disturb both Sebastian's family and the fragile European peace.