This series shines a spotlight on the influential builders, dreamers and believers whose feats transformed the United States, a nation decaying from the inside after the Civil War, into the greatest economic and technological superpower the world had ever seen. The Men Who Built America is the story of a nation at the crossroads and of the people who catapulted it to prosperity. In the first episode, Cornelius Vanderbilt grows from a steamboat entrepreneur to the head of a railroad empire, and gets into a heated rivalry with Jim Fisk and Jay Gould; the up and coming John D. Rockefeller founds Standard Oil. Many business owners lay their own rail lines which leads to the Panic of 1873. Later, Rockefeller starts to expand his wealth by diverting his business from the railroads to a new innovation, oil pipelines.

Experts suspect that the dinosaurs were wiped out after a city-sized asteroid smashed into the Gulf of Mexico causing a huge crater. But until now, they haven't had any proof. In a world first, evolutionary biologist Ben Garrod joins a multi-million pound drilling expedition into the exact spot the asteroid hit to get hard evidence of the link. The team overcomes huge obstacles as it attempts to drill 1,500 metres beneath sea level to pull up rock from the Chicxulub crater. Meanwhile, paleopathologist Professor Alice Roberts travels the globe meeting top scientists and gaining exclusive access to a mass fossil graveyard in New Jersey - believed to date from the same time the asteroid hit. Alice also treks by horseback across the remote plains of Patagonia, to see if the effects of the asteroid impact could have wiped out dinosaurs across the world - almost immediately.

In the last episode, Iain discovers the remarkable impact of just one plant: grass. On the savannah of South Africa he sees how grass unleashed a firestorm to fight its greatest enemy, the forests. He shows how cutting your finger on a blade of grass shows us how it transformed life in the oceans. In Senegal, he meets the cleverest chimps in the world. And, in the ruins of the oldest temple on Earth, he tells the extraordinary story of how grass triggered human civilisation.

In the last episode, in the years after Steven and Brendan's very public trials, the various members of the Avery family struggle to mend their broken lives.

At first glance, Matthew Vandyke —a shy Baltimore native with a sheltered upbringing and a tormenting Obsessive-Compulsive Disorder diagnosis— is the last person you’d imagine on the front lines of the 2011 Libyan revolution. But after finishing grad school and escaping the U.S. for 'a crash course in manhood,' a winding path leads him just there. Motorcycling across North Africa and the Middle East and spending time as an embedded journalist in Iraq, Matthew lands in Libya, forming an unexpected kinship with a group of young men who transform his life. Matthew joins his friends in the rebel army against Gaddafi, taking up arms (and a camera). Along the way, he is captured and held in solitary confinement for six terrifying months.

In the ninth episode, Steven's trial is over, but a new one is just beginning. Will the jury find the suspect's confession or his conflicting statements more believable?