Odds are excellent that extraterrestrial life exists. So why haven’t we found aliens out in the galaxy? Are we looking in the wrong places? New research shows we should look closer to home, even inside our bodies. It turns out that a lot of our DNA is from a mysterious, nonhuman source. Theoretically, alien microbial life can make the journey to Earth from distant worlds, and scientists are finding some unearthly microbes in our upper atmosphere. Could it be from outer space? Could we be part alien? It’s even possible alien life is already here as digital life forms, hiding inside our technology.

Our galaxy is one of hundreds of billions in the universe. View of universe through the Hubble telescope and go back almost all the way to the Big Bang.

Take a tour of the cosmic hot zones--black holes, galaxy mergers, gamma ray bursts and magnetars. Super black holes can literally lasso Earth out of the solar system. A clash between two galaxies can result in a ritual called galactic cannibalism. Magnetars are a cosmic magnetic force so strong it could wipe out data on every credit card.

We used to think that Earth was at the centre of the universe, but now we know we're not even at the centre of our own galaxy. Countless wonders exist between where earth is situated and the massive black hole at the galactic centre of our galaxy. Within the Milky Way can be found the debris of old, dying stars fuelling the birth of new stars and at the galactic centre hypervelocity stars get catapulted clear beyond the Milky Way's outer rim at unimaginable speeds. Come along for a guided tour of 100,000 light-year-wide family of stars and stellar phenomena we call The Milky Way.

Take a tour through the Art Gallery of the Galaxy and view what are considered the "crown jewels" of the heavens. Nebulas are mysterious clouds of gas that aren't classified as stars, planets, moons or asteroids. Astronomers use the most sophisticated techniques to view them since they are practically invisible to the naked eye. Nothing less than stunning, nebulas glow, reflect or obscure the galaxy's light with amazing swirls of color. Nebulas mark the regions where the nothingness of space first coalesces, where stars are born and where stars die. Cutting-edge computer graphics are used to bring the universe down to earth.

The episode begins with Tyson describing how pattern recognition manifested in early civilization as using astronomy and astrology to predict the passing of the seasons, including how the passage of a comet was often taken as an omen. Tyson continues to explain that the origin of comets only became known in the 20th century due to the work of Jan Oort and his hypothesis of the Oort cloud. Tyson then continues to relate the collaboration between Edmond Halley and Isaac Newton in the last part of the 17th century in Cambridge. The collaboration would result in the publication of Philosophiæ Naturalis Principia Mathematica, the first major work to describe the laws of physics in mathematical terms, despite objections and claims of plagiarism from Robert Hooke and financial difficulties of the Royal Society of London. Tyson explains how this work challenged the prevailing notion that God had planned out the heavens, but would end up influencing many factors of modern life, including space flight. Tyson further describes Halley's contributions including determining Earth's distance to the sun, the motion of stars and predicting the orbit of then-unnamed Halley's Comet using Newton's laws. Tyson contrasts these scientific approaches to understanding the galaxy compared to what earlier civilizations had done, and considers this advancement as mankind's first steps into exploring the universe. The episode ends with an animation of the Milky Way and Andromeda galaxies' merging based on the principles of Newton's laws.