Sunset over the plains of Kenya's Maasai Mara, one of Africa's most protected wild spaces. And home to the fastest land animal on Earth, the cheetah. These agile cats have always been thought of as daylight hunters. They target prey from more than a kilometre away and chase it down at over 100 kilometres an hour. In one of these plains, two cheetah brothers attempt a high-speed night hunt with a gang of powerful hyenas on their trail.

What sort of alien civilizations might exist in the vastness of space? Terra is the fictional world imagined in Episode 4, a planet nine billion years old, twice as old as Earth. Old enough that a truly advanced intelligence could evolve. It was once a fertile world, now it is barren. But life can still thrive here in artificial domes. Over time, they've evolved not to need their bodies. They exist only as neural tissue. They never age, they never die. They're monitored and maintained by robots.
If alien civilizations are statistically so likely, why haven't astronomers found any sign of them? Where is everyone? Every time we look at an individual star, that's like dropping a bucket in the ocean. We're going to have to look at a lot of stars and to search through a lot of data until we find the clue that leads us to another civilization.

The series, depicted by state of the art CGI techniques, and applying the laws of life on Earth to the rest of the galaxy, blends fact with science fiction and conceptualizes what alien life might be like on other planets.
In the prologue, astronomer Didier Queloz makes an appearance to discuss the discoveries of exoplanets and how they are analyzed in the real world. In Episode 1, the fictional world imagined is Atlas, a world with higher gravity than Earth and a thicker atmosphere leading to airborne creatures. In explaining the aliens of Atlas, the episode also explores the handicap principle in insects, and shows a rehabilitative form of falconry as captive falcons are trained to live in the wild.

Even 2,000 years after his death, General Hannibal's battle strategies are still studied today. But of all his military feats, perhaps his greatest was leading his massive Carthaginian army of men and three-dozen elephants across the Alps and into the heartland of Rome in 218 B.C. Until now, the route they took has been a matter of dispute, but thanks to modern-day technology, geomorphologist Bill Mahaney and microbiologist Chris Allen believe they've accurately traced this ancient journey.

The fourth episode starts off with the two riding through Santa Cruz, Argentina. The plan is to cross over into Chile and then going up into the Andes. Ewan and Charley head through Argentina’s red rock landscape while a member of their team copes with altitude sickness. The duo are well and truly underway and the first signs of all are well is how well the Harleys hold up in challenging conditions. The roads alternate between unforgiving and pleasant and these e-bikes push through effortlessly. As they ride through Chilean Andes, the audience is shown a picturesque view of the beauty of the countryside, an experience which Boorman calls 'magical.'

Ewan, Charley, and the team land in Ushuaia, the southernmost tip of South America, but tensions arise due to snow and mechanical issues. Traveling 13000 miles over 100 days on electric bikes is hard to imagine. Ewan McGregor and Charles Boorman find out how challenging their mission is as they embark on a journey on prototype Harley Davidsons and the Rivian trucks. The first obstacle is electricity. While parts of the city have no problems with charging the bikes and the trucks, the countryside is where the duo face issues.