The series is a re-examination of some of the under-reported and darkest parts of American modern history using little known documents and newly uncovered archival material, looking beyond official versions of events to the deeper causes and implications and exploring how events from the past still have resonant themes for the present day. This episode addresses the historical backround, consequences and reasons behind the use of atomic bombs against the Japanese in the second world war.

The human brain is the most complex object we’ve discovered in the universe, and every day much of its neural circuitry is taken up with the tens of thousands of decisions we need to make. ‘How do I decide?’ is a journey through the unseen world of decisions, and how they get made. Decisión-making is what allows us to navigate a course through life. Discover how important emotions are in making decissions and, as we learn more about our own brains, we can break away from slavery to our impulses. Neuroscience shows that you're made up of multiple competing drives and by understanding how choices battle it out in the brain, we can learn how to make better decisions.

'Crude Awakening'- To combat the worst environmental disaster in American history, BP and the Coast Guard dumped nearly 2 million gallons of a chemical dispersant called Corexit into the Gulf. But instead of helping clean up the spill, Corexit made things worse. Shane Smith heads to Louisiana to report on the lasting effects of the BP oil spill. 'The Enemy of My Enemy' - Yemen, the fractured state in the Arabian peninsula, is at the top of the worry list for President Obama's national security team, and the rise of Al Qaeda there is only half the reason why. The real trouble is a current threat posed by the little-known Houthi rebel movement in the north of the country - a grassroots army, allegedly funded by Iran, that has never granted access to any other Western film crew before. Ben Anderson goes deep into Houthi-controlled territory to learn about the group that's fighting, and beating, Al Qaeda in the east, Saudi Arabia in the north, and Yemen's central government in the south.

It was 1985. Guns N' Roses were soon to be known as the last mammoth rock entity to come out of LA after selling over 100 million albums. Jon Brewer brings alive never-before-seen video footage of Guns N' Roses in their earliest days as a fledgling band, filmed and meticulously archived over the years by their close friend. They became known as 'the most dangerous band in the world' and retained the title for reasons this film portrays, via interviews with band members and those who were there on, and off, tour. Venture down seedy Sunset Strip to the Whiskey, the Rainbow and the Roxy, all known as 'the Jungle'.

Diarmaid MacCulloch's own life story makes him a symbol of a distinctive feature about Western Christianity - scepticism, a tendency to doubt which has transformed both Western culture and Christianity. In the final programme in the series, he asks where that change came from. He challenges the simplistic notion that faith in Christianity has steadily ebbed away before the relentless advance of science, reason and progress, and shows instead how the tide of faith perversely flows back in. Despite the attacks of Newton, Voltaire, the French Revolutionaries and Darwin, Christianity has shown a remarkable resilience. The greatest damage to Christianity was actually inflicted to its moral credibility by the two great wars of the 20th century and by its entanglement with Fascism and Nazism. And yet it is during crisis that the Church has rediscovered deep and enduring truths about itself, which may even be a clue to its future.

Al-Khalili travels to northern Syria to discover how, a thousand years ago, the great astronomer and mathematician Al-Biruni estimated the size of the earth to within a few hundred miles of the correct figure. He discovers how medieval Islamic scholars helped turn the magical and occult practice of alchemy into modern chemistry. In Cairo, he tells the story of the extraordinary physicist Ibn al-Haytham, who helped establish the modern science of optics and proved one of the most fundamental principles in physics - that light travels in straight lines. Prof Al-Khalili argues that these scholars are among the first people to insist that all scientific theories are backed up by careful experimental observation, bringing a rigour to science that didn't really exist before.