In 'Gun School' we visit the New Life Baptist Church & Academy in Albuquerque, NM, where Pastor Larry Allen preaches guns and teaches guns. In 'Toxic Iraq', after ravaging Iraq over the past decade, the U.S. is finally exiting the country, leaving behind a toxic cesspool of military waste.

The dome that crowns Florence's great cathedral of Santa Maria del Fiore, the Duomo, is a masterpiece of Renaissance ingenuity and an enduring source of mystery. Still the largest masonry dome on earth, it is taller than the Statue of Liberty and weighs as much as an average cruise ship. Historians and engineers have long debated how its architect, Filippo Brunelleschi, kept the dome perfectly aligned and symmetrical as the sides rose and converged toward the center." More than four million bricks could collapse at any moment -- and we still don't understand how Brunelleschi prevented it. To test the latest theories, a team of U.S. bricklayers will help build an experimental "mini-Duomo" using period tools and techniques.

'The Coldest War': With the polar ice caps shrinking due to global warming, new trade routes are being exposed, along with billions of dollars' worth of natural-resource reserves. The five nations bordering the Arctic are readying themselves to fight for it. The problem is that there's one non-NATO country that already considers itself rightful owner of the region: Russia. With Vladimir Putin's recent military annexation of Crimea, there's a definite possibility its aggressions will boil over, returning the international community to precarious Cold War footing. We will head north to witness NATO forces participating in the largest polar military exercise in history. 'Heroin Warfare': Since the U.S. occupation of Afghanistan, heroin production in the region has skyrocketed, making the country the number-one producer by a large margin. Though Iran, Afghanistan's neighbor, is an ultraconservative country, Afghan heroin flowing across the border has actually caused Iran to have the worst heroin use problem in the world. Suroosh Alvi gets a rare look inside Iran to meet the suffering heroin addicts, and see how the country is coping with the illegal drug trade.

During the chaotic final weeks of the Vietnam War, the North Vietnamese Army closes in on Saigon as the panicked South Vietnamese people desperately attempt to escape. On the ground, American soldiers and diplomats confront the same moral quandary: whether to obey White House orders to evacuate U.S. citizens only--or to risk treason and save the lives of as many South Vietnamese citizens as they can.

In 2006, an Iceland-based outfit called The Sunshine Press launched the website WikiLeaks.org. As run by Australian Internet activist Julian Assange, the site's mandate involved regularly publishing top-secret documents and covert information, often regarding governments and their respective military operations". As might be expected, this set off a firestorm between those who admired the organization's bravado and resourcefulness, and those who argued, not unjustly, that the dissemination of data regarding such events as the U.S. war in Afghanistan could put untold numbers of lives at risk. In We Steal Secrets, Gibney relays the story of the WikiLeaks website from the inside, and moves beyond black and white to penetrate a complex network of activity guided by courage and idealism but also allegedly guilty of ethical insensitivity and hypocrisy. Acclaimed documentarian Alex Gibney (Enron: The Smartest Guys in the Room) takes the reins for this no-holds-barred look at one of the most unusual phenomena of early 21st century media.

Widespread immigration to the U.S. from Latin countries begins – first with a small group from Cuba, then a larger one from Mexico. Both flee chaos and violence in their home country and are attracted by opportunities in the United States. In 1898, the U.S. helps liberate Cuba and Puerto Rico from Spain but then seizes Puerto Rico as its colony. The first Puerto Rican arrivals (now U.S. citizens) establish a network in New York.