The Cave of Swallows in Mexico is a 400m vertical shaft, deep enough to engulf the Empire State Building. The Lechuguilla cave system in the USA is 193km long and 500m deep with astonishing crystal formations hanging from its chambers. Although often overlooked, caves are remarkable habitats with equally bizarre wildlife. Cave angel fish cling to the walls behind cave waterfalls with microscopic hooks on their flattened fins. Cave swiftlets navigate by echo-location and build nests out of saliva. The Texas cave salamander has neither eyes nor pigment. Unique access to a hidden world of stalactites, stalagmites, snotites and troglodytes brings a wealth of surprises.

Is mankind alone, or are there aliens out there, either waiting to be discovered, or on their way to find Earth? Professor Brian Cox spends this episode asking such questions, and what he discovers may raise a few eyebrows. He begins by exploring the human race's efforts to find neighbours in outer space, including the launch of two golden discs containing a greeting from Earth in the 1970s; they are still travelling and are now the most distant man-made objects from the planet. Brian also meets members of the Search for Extra-Terrestrial Intelligence, who have been monitoring radio signals for 50 years without success, before discussing the ingredients needed to make an intelligent civilisation with astrophysicist Dr Frank Drake.

Academy Award-winning director Alex Gibney (Taxi to the Dark Side) masterfully explores the fall of the disgraced cycling champion following the 2009 Tour de France, making use of his extraordinary access to attain rare interviews with former teammates, alleged doping mastermind Dr. Michele Ferrari, and Armstrong himself. What was Lance Armstrong thinking? For years, after seizing international fame as the cancer survivor who won seven Tour de France titles, he fiercely denied accusations that he used performance-enhancing drugs. He used his power to aggressively litigate journalists and publicly humiliate former friends who claimed otherwise. His deceit finally cracked in January 2013, when he admitted guilt to Oprah Winfrey in a television interview that critics decried for only scratching the surface. Academy Award-winning director Alex Gibney approaches Armstrong with unique and extraordinary access. In 2009, Gibney was commissioned to make a film about Armstrong's return to the Tour de France, four years after the racing champion had declared retirement. That race would later stir up devastating evidence in the case against Armstrong. But Gibney came away from the experience unable to reconcile the discrepancy between doping allegations and Armstrong's emphatic denials. Then, post-Oprah, Gibney went back to Armstrong for new interviews to extract a more detailed account of his double life. In The Armstrong Lie, Gibney masterfully explores the complexities of the case, interweaving the dramatic action of the 2009 Tour de France, when Armstrong found himself unexpectedly competing against his own teammate Alberto Contador. Gibney attains rare interviews with Armstrong's former teammates and alleged doping mastermind Dr. Michele Ferrari. The film also raises troubling questions about the process of doping regulation. Recently, when asked to give advice to documentary filmmakers, Gibney responded with a motto exemplified by this film: "Embrace contradictions."

the rise and fall of a tech industry prodigy. Interviews with his friends and loved ones paint a portrait of Swartz as a martyr of freedom of information and hail his fight for the public's right to access tax-funded academic and scientific research, culminating in a personally devastating two-year Federal lawsuit." An avid researcher who had previously accessed otherwise private databases, Swartz, acting "in the grand tradition of civil disobedience to declare... opposition to this private theft of public culture" used MIT computers to access tax-funded research that would otherwise be held privately by for-profit publishers, an incident many viewers may remember from national headlines just a few year ago. Though neither MIT nor the digital repository Swartz accessed pressed charges, a US Attorney stepped in and filed a 13-count felony charge against Swartz, threatening him with over $1 million in fines and up to 35 years of jail time. Despite the defense of his peers, these events launched Swartz into a two-year long downward spiral of withdrawal and depression. Aaron Swartz's untimely death at the age of 26.