Quinto sets out to discover whether aliens exist and what evidence we have to prove it. He meets with several who say they have encountered extra-terrestrial life–a man who has been abducted by aliens several times since childhood; a man who claims to have extracted an alien implant; and a woman who shows Zachary what it feels like to be abducted into a spacecraft.
Zachary also meets with the world's leading scientists at SETI in Green Banks, West Virginia. There, utilizing the world's largest telescope, they show him the methods they employ to communicate with potential other-worldly visitors and what this research has taught them about a mysterious radio signal they picked up 3 billion light years away.

Everywhere you go, you generate a cloud of data. You're trailing data, everything that you do is producing data. And then there are computers looking at that data that are learning, and these computers are essentially trying to serve you better. They're trying to personalize things to you. They're trying to adapt the world to you. So on the one hand, this is great, because the world will get adapted to you without you even having to explicitly adapt it. There's also a danger, because the entities in the companies that are in control of those algorithms don't necessarily have the same goals as you, and this is where I think people need to be aware that, what's going on, so they can have more control over it.
We came into this new world thinking that we were users of social media and search engines. It didn't occur to us that social media and search engines were actually using us.

With much of it covered in ice all year round and with no daylight from October to March, the Arctic Ocean is one of the world's most remarkable oceans. Its home to a multitude of unique life forms, all highly adapted to cope with the extreme and seasonal conditions. The impacts of climate change are more strongly felt here than anywhere else in the world.

Everyone always wants to be able to choose - but who really makes these choices? And do we really want to have more choices? Michael Stevens finds out as he explores decision-making.

While scientists have previously theorised about a “Big Crunch” where the universe retracts back to its original size, the discovery of Dark Matter and Dark Energy has placed that hypothesis on the backburner. Some astronomers now believe that if Dark Matter offsets Dark Energy then as the universe slowly expands, stars will gradually fade, running out of fuel and leading to a dark, cold and lifeless universe. Others hypothesise a much more violent end where Dark Energy continues to expand the universe at a greater and greater speed. Stronger than gravity, Dark Energy would pull apart everything down to the fundamental particles – the universe’s very fibres. While the universe’s end may be 50 billion years away, great leaps in science will continue to alter how we believe the universe was formed – and how it will end.

The day of the Nazaré competition has arrived, and Garrett McNamara decides not to compete but instead support his long-time friend and teammate Andrew 'Cotty' Cotton. The competition does not go smoothly, with a major accident that has secondary effects on Cotty. After the competition, Garrett tries surfing at Nazaré again and realizes that can resume big-wave surfing. The episode concludes with retrospectives from a number of the surfers who appeared on various episodes throughout the season.