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.

In Baltimore, home of the first railroad in the United States, he discovers how the first American steam engine owed much to pioneering British technology and how a historic telegraph message was received.

Michael investigates race relations in the troubled city, taking a drive downtown with a former drug dealer, now a teacher. On the city's beautiful east coast, Michael discovers the impressive star-shaped Fort McHenry and learns how the Star Spangled Banner national anthem was born.

Medics at the city's Johns Hopkins Hospital show Michael how their institution has grown from its 19th-century foundation by the railroad magnate into a world-leading centre for healthcare. And at the city's Lexington Market, Michael learns what gives a Maryland crab cake the edge.