This episode sees naturalist Chris Packham assess the lives of the 20th century's greatest scientists. Chris examines the lives of Marie Curie, Albert Einstein, Alan Turing and Tu You You. He explores some of their most famous discoveries - as well as the lesser known human stories behind them - so often overshadowed by the scale and impact of their work.

In the 20th century, advancements in science saw life expectancy double; they helped us advance technology in a way which would have been unimaginable just years before - they even meant we shook off gravity and left the Earth itself. The story of science in the 20th century is interwoven with some of the most urgent moments in the history of humanity, from wartime innovations that have cost - and saved - the lives of millions, to the worldwide fight against disease, and the battles to understand the very fabric of the universe.

The four icons examined by this documentary each made significant contributions to mankind, but each was, in a way, an outsider. These icons were marginalised or persecuted for different reasons, be it their sexuality, gender or background - but they do share something in common. They were all people with the temerity to cast off the shackles of conventional thought and received wisdom, and to dare to approach things differently. What this film makes clear, is that these are not dusty and lifeless figures of the lab, but extraordinary human beings who often huge sacrifices for their work. They came from different fields - from medicine, chemistry, physics, and mathematics - but humanity owes each of them a great debt.

Marie Curie discovered new elements, pioneered radiotherapy and was one of the first to examine the sub-atomic world, before a scandal saw her adopted homeland turn its back on her. Years later, France would owe her an enormous debt when she took to the front lines of the First World War with a fleet of mobile X-ray units.

Einstein was a physicist who rewrote the rules of the universe. Hounded from his native Germany by the Nazis and fearful of what they were capable of, he advocated the development of atomic weapons - before desperately trying to convince the US to abandon them once the threat had passed. He spent the rest of his life as a tireless campaigner for peace and freedom.

A genius of mathematics, Turing developed machines which were the forerunners of modern computers. Called upon to help crack Nazi codes, his work at Bletchley Park would prove decisive in the war effort. Later, society would repay Turing by prosecuting him for being gay and sentencing him to barbaric hormone treatment.

Working at a time when Mao's cultural revolution put scientists at risk of persecution, brutality and even death, Tu You You was tasked with working on a secret project to search for a cure for malaria. She discovered Artemisinin - later transformed into a drug which has saved millions of lives but was then almost written out of history.

At the end of the programme, the public vote for the greatest scientist of the century, who, along with the finalists from the other categories, are put through to the live final at the end of the series. Show less