Armed with his Appleton's Guide, Michael Portillo reaches a milestone on his American journey: the boundary between the northern and southern states, known as the Mason-Dixon line. He discovers the origins of what became, for black Americans, the border between slavery and freedom in an 18th-century English dispute over land. On the heritage Wilmington and Western Railroad, Michael meets Phoebe Snow, created to reassure passengers that clean burning coal wouldn't make their clothes dirty. Michael uncovers the explosive history of gunpowder production in Delaware and then takes a boat trip up the Susquehanna River, following the route taken by one of the first English settlers, John Smith.