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.

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?

In the second episode, Andrew Carnegie builds an empire around steel, but finds himself struggling to save face after the ruthless tactics of his business partner, Henry Frick, result in both the Johnstown Flood as well as the bloody 1892 strike at the Homestead Steel Works.

J.P. Morgan proceeds to banish the dark with the direct current electric light of Thomas Edison, but the two soon face serious competition from the alternating current of George Westinghouse and Nikola Tesla. As the 19th century comes to a close, the titans of industry must try to work together to stop a new threat in budding politician William Jennings Bryan, who threatens to dissolve monopolies in America.

Rockefeller, Carnegie and Morgan team up to help elect William McKinley to the U.S. presidency by paying for his 1896 campaign, to avoid a possible attack on monopolies. However, fate intervenes when McKinley is suddenly assassinated, and vice president Theodore Roosevelt assumes the presidency and promptly begins dissolving monopolies and trusts in America. Meanwhile, Morgan buys out Carnegie Steel to make Carnegie the richest man in the world, and Henry Ford designs an affordable automobile with his Model T and starts his own business, Ford Motor Company, which sets a new business model for companies to follow.