A fifth of the land on our planet is covered by desert. Deserts may appear to be barren and empty, but they are of crucial importance to life. For those that can overcome their challenges they provide a vital refuge. The Grasslands are one of our planet's most productive landscapes. They support the greatest aggregations of large animals on Earth. Cameras follow desert elephants seeking sustenance, bison roaming North American grasslands and caterpillars living the good life underground.

The last episode examines the fragile interdependence that exists between forests' wide variety of residents, including bald eagles, hunting dogs and Siberian tigers.
Over half of all the world's trees, evergreen and deciduous, stand in great assemblies. For many of us, they are places of mystery and darkness. They are key to our climate, and home to countless unique species. The boreal forest contains 750 billion trees, and it stores over 40 percent of the world's carbon, making it a vital element in the fight against climate change. In the past, we have destroyed them without hesitation. Yet, forests do have an astonishing ability to recover. If we choose to give forests time and space, they could reclothe the earth with much of the rich and varied communities of animals and plants of which we have, so recently, robbed it. A future with more forests is key to the resilience of our planet.

Foo Fighters prepare to record at the Austin City Limits Studio, with blues guitarist Gary Clark, Jr. In this episode is examined the roots of Austin's music scene, with interviews featuring Billy Gibbons from ZZ Top, and Roky Erickson from 13th Floor Elevators, who is considered one of the American fathers of psychedelic rock. Dave also chats with Terry Lickona, the executive producer of Austin City Limits. The song 'What Did I Do? / God As My Witness' is recorded during this chapter.

Putin returns to power under a storm after a four-year absence, but his attempts to improve his popularity are hobbled by accusations of corruption. The final part of this sinister history doesn’t quite come up to date with Vladimir Putin’s recent moves to 'reset' the Russian constitution so he can rule, theoretically, until at least 2036 – longer than Stalin. But it does walk us through some of his other moves to entrench power, including vote-rigging in parliamentary elections that was so brazen, his approval ratings fell amid mass street protests. Leading the protests was opposition leader Boris Nemtsov, who was then simply gunned down on a street near the Kremlin.
These days, we are told, the world stage interests Putin more than the Russian one, and with various 'mini-Putins' installed around the world, his legacy looks safe.

Los Angeles' highly influential position in rock history is examined. Pat Smear remembers the days of Germs, and visits legendary KROQ disc jockey Rodney Bingenheimer, owner of a 1970s Sunset Strip club that became the hub for the Los Angeles glam rock scene. Foo Fighters head to the desert to record their new song 'Outside', which features a solo from Eagles' guitarist Joe Walsh, at Rancho De La Luna, and in turn, Kyuss and the 1990s Palm Desert Scene is explored.

Episode 3 continues to show the obstacles faced with charging electric bikes in remote places, but Ewan McGregor and Charley Boorman start to learn and evolve their process. The risk of cold temperatures is high but they bravely do it anyway. The duo is having a hard time of it out there but, thankfully, the scenery is absolutely stunning. Heading through Patagonia, Ewan and Charley stay at an eco-lodge in one of the world’s remotest areas with people that live off the grid.