The theory of Némesis, a star that orbits the Sun and causes catastrophic events is explored. Nemesis is a hypothetical red dwarf or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU (1.5 light-years) somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years.

After filming for three years, Planet Earth finally captures the shy Mongolian gazelle. Only a handful of people have witnessed its annual migration. Don't miss the bizarre-looking Tibetan fox, captured on film for the first time. Over six weeks the team follow a pride of 30 lions as they attempt to hunt elephants. Using the latest night vision equipment, the crew film the chaotic battles that ensue at close quarters.

Silk is the invertebrates' great invention, used in a range of ways from from the protective stalks of lacewing eggs to the amazing hanging threads of New Zealand's 'glow worms'. Spiders, though, have taken silk-spinning to extremes. The common wolf spider has no web, but the female is a gentle parent, encasing her eggs in silk and carrying the precious bundle wherever she goes. The bolas spider uses a ball of sticky silk soaked in a copy of moth pheromone to lure its prey. Millions of communal spiders live and feed together in a vast, towering web - an arachnophobe's nightmare.

the final episode deals with plants that live in hostile environments. Attenborough visits Ellesmere Island, north of the Arctic Circle, to demonstrate that even in a place that is unconducive to life, it can be found. Algae and lichens grow in or on rock, and during summer, when the ice melts, flowers are much more apparent. However, they must remain close to the ground to stay out of the chilling wind. In the Tasmanian mountains, plants conserve heat by growing into 'cushions' that act as solar panels, with as many as a million individual shoots grouped together as one. Others, such as the lobelia in Mount Kenya, have a 'fur coat' of dense hairs on their leaves. The saguaro cactus in the Sonoran Desert flourishes because of its ability to retain vast amounts of water, which can't be lost through leaves because it has none. Many desert dwellers benefit from an accelerated life cycle, blooming rapidly within weeks after rainfall. Conversely, Mount Roraima is one of the wettest places on Earth. It is a huge sandstone plateau with high waterfalls and nutrients are continuously washed away, so plants have to adapt their diet if they are to survive. A bladderwort is shown invading a bromeliad. Inhabitants of lakes have other problems to contend with: those that dominate the surface will proliferate, and the Amazon water lily provides an apt illustration. Attenborough ends the series with an entreaty for the conservation of plant species.

An unconventional biography about an Indian Swami who brought yoga and meditation to the West in the 1920s. This feature documentary explores the life and teachings of Paramahansa Yogananda, who authored the spiritual classic Autobiography of a Yogi, which has sold millions of copies worldwide and is a go-to book for seekers, philosophers and yoga enthusiasts today. It was the only book that Steve Jobs had on his iPad, and he arranged to give away 800 copies of it to the dignitaries who attended his memorial service. It was also a point of entry into Eastern mysticism for George Harrison, Russell Simmons and countless yogis. By personalizing his own quest for enlightenment and sharing his struggles along the path, Yogananda made ancient teachings accessible to a modern audience, attracting many followers and ultimately helping millions of seekers today to turn their attention inwards, bucking the temptations of the material world in pursuit of self-realization.

In 1927, Prohibition agent Eliot Ness narrowly escapes a hit ordered by Al Capone. Determined to prove to Capone that he's not intimidated, Ness and his team of Untouchables execute a series of high-profile raids on Capone's breweries. Over the course of a few months, they destroy more than 200,000 gallons of beer, worth a modern-day equivalent of $134 million - and the newspapers cover it all. Capone lashes out against Ness in the press. What Capone doesn't realize is that Ness and the Prohibition agents aren't the only ones trying to take him down. For the past four years, another government agency with more manpower and resources than Ness has been going after the infamous kingpin: the Internal Revenue Service.