Series concludes with the focus shifting to the United States in the post-war years of the 1950s and beyond. Beginning with arguably the most notorious work of 20th century classical music, John Cage's 'silent' composition 4'33", it looks at how a series of maverick Americans re-invented the sound of classical music into a more simple form, bringing back harmonies and rhythms that made it increasingly popular with audiences across the world. It also examines how this music found its way into a spiritual realm, with the strain of pared-down religious composition that came to be known as 'holy minimalism'. From the Maverick concert hall in Woodstock, New York to an Orthodox cathedral in Estonia to a car park in Peckham, south London, the story is told by a stellar line-up of contributors including Philip Glass, Steve Reich, John Adams, Arvo Pärt and John Tavener.

To fly like a bird, Earthflight not only captured remarkable images of wild flocks but also relied on some extraordinary relationships between people and birds. Filmed over four years, in six continents and more than 40 countries, the Earthflight team used many extraordinary techniques. For some of the unique flying shots, members of the team became part of the flock. The birds followed wherever they went - even in a microlight over Edinburgh and London. In Africa, paragliders floated alongside wild vultures, while a model vulture carried a camera inside the flock. In South America, wild-living macaws, that were rescued as babies, still come back to visit their 'foster mother' as he travels along a jungle river. In Africa, a radio-controlled 'drone' silently infiltrates masses of pink flamingos without disturbing a feather, and microlights and helicopters capture the dramatic moment white storks arrive over Istanbul. In Africa a tame vulture carried a camera across the African bush and recreated the behaviour of his wild relatives. Similarly, in the USA, a flock of hand-reared snow geese followed the migration route of wild flocks and took in the sights and sounds of New York - managing to get lost in Brooklyn

Dr Aleks Krotoski concludes her investigation of how the World Wide Web is transforming almost every aspect of our lives. Joined by Facebook founder Mark Zuckerberg, Bill Gates, Al Gore and the neuroscientist Susan Greenfield, Aleks examines the popularity of social networks such as Facebook and asks how they are changing our relationships. And, in a ground-breaking test at University College London, Aleks investigates how the Web may be distracting and overloading our brains.

Pet Shop Boys' Neil Tennant and Chris Lowe are the most successful duo in UK Music history. They have sold more than 50 million records, produced over 40 Top singles, four UK number ones, performed in several world tours, and they are still making new music together.
In April this year, Pet Shop Boys are releasing a new album which comes 40 years after the original release of their classic song West End Girls. IMAGINE... is given a sneak preview of the album and talks to Tennant and Lowe about its creation and their evolution over the past four decades: pioneering, original, highly influential but always maintaining the integrity and quality of their inimitable style, sound and songwriting.
Their songs have often commented on Britain and the world around them with wit, sensitivity and intelligence driving the stories they want to share through some of the most memorable synth-pop music ever created. For their tours they have worked with the most innovative theatre personnel to create original and thrilling performances. Now for the first time they have allowed backstage access as IMAGINE... accompanies them on their global Dreamworld tour, filming rehearsals in London and backstage in Helsinki.

Written and presented by David Attenborough, who said: 'One of the most wonderful things about filming plants is that you can reveal hidden aspects of their lives, you can capture the moment as one plant strangles another, and as they burst into flower. But whilst time-lapse photography allows you to see things that no human being has ever seen before". David begins his journey inside the magnificent Palm House, a unique global rainforest in London. Here, he explores the extraordinary plants that are so well adapted to wet and humid environments and unravels the intimate relationships between wet zone plants and the animals that depend on them. It was in the wet zones of the world that plants first moved on to land and in the Waterlily House David reveals how flowers first evolved some 140 million years ago. Watching a kaleidoscope of breath-taking time-lapses of these most primitive of flowers swelling and blooming in 3D, he is able to piece together the very first evolutionary steps that plants took to employ a wealth of insects to carry their precious pollen for the first time. David discovers clues to answer a question that even had Charles Darwin stumped: how did flowering plants evolve so fast to go on to colonise the entire planet so successfully?

Julien Temple's epic time-travelling voyage to the heart of his hometown. From musicians, writers and artists to dangerous thinkers, political radicals and above all ordinary people, this is the story of London's immigrants, its bohemians and how together they changed the city forever. Reaching back to the dawn of film in London at the start of the 20th century, the story unfolds through film archive, voices of Londoners past and present and the flow of popular music across the century; a stream of urban consciousness, like the river which flows through its heart. It ends now, as London prepares to welcome the world to the 2012 Olympics.