The film begins when journalist Craig Leeson, searching for the elusive blue whale, discovers plastic waste in what should be pristine ocean. In this adventure documentary, Craig teams up with free diver Tanya Streeter and an international team of scientists and researchers, and they travel to twenty locations around the world over the next four years to explore the fragile state of our oceans, uncover alarming truths about plastic pollution, and reveal working solutions that can be put into immediate effect.

Just under 200 years ago scientists discovered something profound, that electricity is connected to another of nature's most fundamental forces - magnetism. In the second episode, Jim discovers how harnessing the link between magnetism and electricity would completely transform the world, allowing us to generate a seemingly limitless amount of electric power which we could utilise to drive machines, communicate across continents and light our homes. This is the story of how scientists and engineers unlocked the nature of electricity in an extraordinary century of innovation and invention.

It's a natural history epic. It's a compelling detective story. It's a scientific adventure at its best. It took Dr Fred Urquhart almost 40 years to discover the monarch butterflies' secret hideaway and prove the most incredible migration on Earth. Following the year-long annual migration cycle of the butterflies, the award-winning production team filmed hundreds of millions of monarchs in their remote overwintering sanctuaries in Mexico in 2011 and again in 2012 and also along their migratory routes from Canada, across the U.S. and into Mexico. The film immerses you in the astounding migration experience as two generations of the butterflies migrate north and then a Super Generation miraculously finds its way from Canada to a few isolated mountaintops in Mexico.

Diarmaid MacCulloch's own life story makes him a symbol of a distinctive feature about Western Christianity - scepticism, a tendency to doubt which has transformed both Western culture and Christianity. In the final programme in the series, he asks where that change came from. He challenges the simplistic notion that faith in Christianity has steadily ebbed away before the relentless advance of science, reason and progress, and shows instead how the tide of faith perversely flows back in. Despite the attacks of Newton, Voltaire, the French Revolutionaries and Darwin, Christianity has shown a remarkable resilience. The greatest damage to Christianity was actually inflicted to its moral credibility by the two great wars of the 20th century and by its entanglement with Fascism and Nazism. And yet it is during crisis that the Church has rediscovered deep and enduring truths about itself, which may even be a clue to its future.

Take a look back at many of the most fascinating science stories of 2017, a year full of stunning advancements in individual fields of study, from astronomy to biology, geology to history – when we piece these discoveries together we see the year in a new light.

In the third part of his journey into the history of Christianity, Professor Diarmaid MacCulloch charts Orthodoxy's extraordinary fight for survival. After its glory days in the eastern Roman Empire, it stood right in the path of Muslim expansion, suffered betrayal by crusading Catholics, was seized by the Russian tsars and faced near-extinction under Soviet communism. MacCulloch visits the greatest collection of early icons in the Sinai desert, a surviving relic of the iconoclastic crisis in Istanbul and Ivan the Terrible's cathedral in Moscow to discover the secret of Orthodoxy's endurance.