The Arctic is the harshest environment on Earth: little food grows, it's dark for months on end, and temperatures stay well below freezing for much of the year. Yet four million people manage to survive here. Human Planet tells remarkable stories of extraordinary people who make their homes in nature's deep freeze. In springtime, Amos and Karl-Frederik set out across the sea ice with their dogs to catch a real-life sea monster: a Greenland shark! Inuit mussel-gatherers venture underneath the sea ice at low tide for a perilous race against time as they gather their food. And the children of Churchill, Manitoba, set out on the most dangerous trick or treating Halloween in the world: they risk coming face-to-face with deadly polar bears on the streets of their town. Who'll get the tastiest snack?

Grasslands feed the world. Over thousands of years, we humans have learned to grow grains on the grasslands and domesticate the creatures that live there. Our success has propelled our population to almost seven billion people. But this episode reveals that, even today, life in the 'Garden of Eden' isn't always rosy. We walk with the Dorobo people of Kenya as they bravely attempt to scare off a pride of hungry lions from their freshly caught kill. We gallop across the Steppe with extraordinary Mongolian horsemen who were 'born in the saddle'. And in a perfect partnership with nature built up over generations Maasai children must literally talk to the birds! The honeyguide leads them to find sweet treats, but they'll have to repay the favour.

Chinese 'Cockblock'. In China, where marrying-age men outnumber women by the millions, discover the lucrative business catered to matchmaking and the bachelors who use such services. 'European Meltdown' With their economy in the toilet and no jobs to be had, Europe's youth are taking to the streets to demand radical changes.

Playing with Nuclear Fire' - In March 2011, the Tohoku earthquake in Japan created a tsunami that killed some 16,000 people and crippled the Fukushima Daiichi nuclear power plant. In the aftermath, the government and TEPCO, the plant's operator, withheld information about the extent of the damage. Three years later, citizens and the international community are left wondering if Japan really does have the situation under control, as the government is insisting, or if the danger is far greater than anyone is willing to admit. 'No Man Left Behind' - It's estimated that over a quarter million vets from recent wars have sought treatment for PTSD. Despite these statistics, veterans often face an uphill battle to get treatment, receiving inadequate attention and, most dangerously, overprescribed narcotics and other pharmaceuticals. Ryan Duffy meets veterans struggling with mental illness and addiction.

When the Second World War ended, the people of liberated Europe celebrated their freedom from Nazi tyranny. Their years of suffering had ended, but for millions of Germans, the end of the conflict opened a new and terrible chapter. They suffered the appalling violence meted out to the defeated, especially to those ethnic Germans who had lived peacefully for centuries in neighbouring countries". Savage Peace uses rare and unseen archive film, the documentary tells a harrowing story of vengeance against German civilians, which mirrored some of the worst cruelty of the Nazi occupiers during the years of war. The Savage Peace includes the unique testimony of eyewitnesses and victims, who recall the horrors with searing clarity, their memories undimmed 70 years after the events took place. This a story that has, until now, been untold amidst the justified celebration of an end to an unspeakable tyranny. But as the writer George Orwell said, the treatment of the defeated Germans was a terrible crime that has gone unpunished.

The key to understanding the universe seems to be understanding its smallest components. But the quantum realm bears little resemblance to the universe we know. Image a particle that can be many places at the same time and communicate changes instantly across vast distances, even to the other side of the Universe. Shrinking down billions of times, into the realm of atoms and sub-atomic particles, takes us into a bizarre world of paradoxes and multiverses. Explore with us quantum physics and the potential applications in computer science.