Sagan reflects on the future of humanity and the question of 'who speaks for Earth?' when meeting extraterrestrials. He discusses the very different meetings of the Tlingit people and explorer Jean-François de La Perouse with the destruction of the Aztecs by Spanish conquistadors, the looming threat of nuclear warfare, and the threats shown by destruction of the Library of Alexandria and the murder of Hypatia. The episode ends with an overview of the beginning of the universe, the evolution of life, and the accomplishments of humanity and makes a plea to mankind to cherish life and continue its journey in the cosmos. The Cosmos Update notes the preliminary reconnaissance of planets with spacecraft, the fall of the Berlin Wall and the end of apartheid in South Africa, and measures towards the reduction of nuclear weapons.

In ‘Who will we be?’ Dr. David Eagleman journeys into the future, and asks what’s next for the human brain, and for our species. We stand at a major turning point, one where we might take control of our own development. We face a future of uncharted possibilities in which our relationship with our own body, our relationship with the world, the very basic nature of who we are is set to be transformed. For thousands of generations, humans have lived the same life cycle over and over. We are born, we control a fragile body, we experience a limited reality, and we die. But science and technology are giving us tools to transcend that evolutionary story. Our brains don't have to remain as we have inherited them. We are capable of extending our reality, of inhabiting new bodies, and possibly shedding our physical forms altogether. And we are discovering the tools to shape our own destiny. Who we become is up to us.

In episode two, Professor Brian Cox is off to India, where he assesses arguably the first evidence of rational thought in literature, the poetry of the Vedic monks. They pondered mankind's origins, realising there must have been a day with no yesterday - a day of creation - prompting the age-old question of where did the universe come from? Brian marvels that the universe seems to follow a set of rules, the laws of physics, allowing space to be considered on the grandest scale, travelling to the most distant, farthest reaches of the cosmos just by using our minds. Brian also visits Japan, and offers viewers the idea that man lives in just one of an infinite number of universes that are being made all the time.

In ‘Why Do I Need You?’ Dr. David Eagleman explores how the human brain relies on other brains to thrive and survive. Our fundamentally social nature can hold the key to our sucdess as a species. Our brains are so fundamentally wired to interact that we are something more like a single vast super-organism. In this age of digital connection, we desperately need to understand how human brains interact if we want our civilization to have a future, if we want to avoid fanaticism and to embrace cooperation. This neural interdependence begins at birth. Dr. David Eagleman invites a group of babies to a puppet show to showcase their ability to discern who is trustworthy, and who isn’t.

The world stood in fear of an emerging new disease that threatened to kill millions. A new flu variant H1N1 had arrived. If this latest pandemic has taught anything, it is just how little is understood about the invisible world of viruses. But that has not stopped scientists trying. Horizon follows the leading researchers from across the world, who are attempting to unravel the many secrets of viruses to understand when and why they kill.

We all agree lying is shameful. Yet we still deliberately deceive each other constantly. Are our brains wired for lying from a young age? The brains of pathological liars may provide insights. Will technology make it easier for us to be dishonest, or could it someday instantly reveal someone is lying? Perhaps we are deceitful because our limited senses prevent us from seeing the real truth. Scientists say our own memories deceive us, and have managed to implant false memories. Other scientists look for ultimate truth in the subatomic world … only to end up turning reality on its head.