A new force threatens our perfect planet. In the past, five mass extinction events were caused by cataclysmic volcanic eruptions. It was not the lava or ash that wiped out life, but an invisible gas released by volcanoes: carbon dioxide. Almost every part of modern life depends on energy created by burning fossil fuels, and this produces CO2 in huge amounts. Humans are changing our planet so rapidly, it’s affecting earth’s life support systems: our weather, our oceans and the living world. The greatest change to be made is in how we create energy, and the planet is brimming with natural power that can help us do just that. It’s these forces of nature - the wind, the sun, waves and geothermal energy - that hold the key to our future.
Through compelling animal-led stories and expert interviews, we discover how CO2 is destabilising our planet. We meet rescued orphaned elephants in Kenya, victims of ever worsening droughts, and join ocean patrols off the coast of Gabon fighting to save endangered sharks. In the Amazon, we witness wildlife teams saving animals in the shrinking forests, and in San Diego we enter a cryogenic zoo preserving the DNA of endangered species before they become extinct.

Ewan and Charley swap their e-Harley Davidsons for plane first and follow it up with a journey by ship to Panama. McGregor's bike needs some repairs and will be fixed by the time they reach Costa Rica. The ship they travel in with the bikes looks like a beaten-down vessel that raises genuine concerns about making the journey in one piece. The boat crew looks sharp and proactive while trying to make the show crew's journey as comfortable and safe as possible. The episode also introduces Nuqui, one of the wettest regions in the world where the ship quickly makes a pitstop to fuel up on essential supplies.

Sam Neill takes the viewer on journeys across the universe. In this episode, we made an exploration of the strange and terrifying world of the universe's ultimate monster - the black hole. Where are they - and is our planet in danger?

Ewan and Charley make their way to Peru from Bolivia, and the scenery is just beautiful. Ewan wanted to visit Machu Picchu since he was a kid and decides to show the world the Incan citadel set high in the Andes Mountains. Next up, they make their way to the Cutivireni, a community of Ashaninka people in the Amazon rainforest, with its carbon program to limit the magnitude or rate of global warming and its related effects.

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.

The Sun is a endless churning cauldron of nuclear reactions and our planet is at its mercy. Revealing its inner workings was once mission impossible, but not any more. We've recruited a fleet of spacecraft that monitor the Sun 24 hours a day, under close surveillance. We just might have what it takes to defend our planet.