Michael 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 Wilmington and Western Railroad, Michael meets the passenger train Phoebe Snow, created by the railroads at the turn of the 20th century to reassure passengers that clean burning coal wouldn't make their clothes dirty. Michael uncovers the explosive history of gunpowder production in Delaware, begun by a Frenchman, whose chateau still stands. He then takes a boat trip up the Susquehanna River following the route taken by one of the first English settlers, John Smith.