Michael Portillo continues his 1,000-mile journey from the northern state of Minnesota to the home of the blues in Memphis, Tennessee. Today, in the nation's rail capital, where tracks pass underground and overground and are elevated into the air, Michael investigates the ultimate marshalling yard. At the ornate Palmer House Hotel, Michael teams up with the head chef to recreate the original chocolate brownie, invented by Bertha Palmer for Chicago's World Exposition in 1893. He discovers the origins of the Sanitary and Ship Canal and uncovers the history of an incredible civil engineering project which raised the city to new heights. Heading deep underground, Michael inspects a modern day scheme on a similarly awesome scale, described by the boss as the largest toilet in the world.