In the summer of 1813, as war with Britain intensified, President James Madison secretly dispatched an envoy to the Regency government of Spain with the urgent goal of thwarting a feared British bid to use Spanish Florida as a base from which to attack the United States, and with the further hope of acquiring that territory for America. The man Madison sent to pursue those challenging tasks was Anthony Morris, a friend of Dolley Madison's from their youth in Philadelphia and a devout Quaker lawyer who had never before journeyed abroad. Morris, a widower, had willingly accepted the president's...