The True Stories strand, which showcases the best international feature documentaries, uncovers the mystery behind a massive explosion that shook Siberia in 1908.The epicentre, Tunguska, was so remote that no-one went in to investigate immediately. The first scientist to eventually visit the site found 80 million uprooted trees lying in neat rows, and thought that a meteor may have been to blame - but failed to find any fragments or crater and so the mystery remained unsolved.One hundred years after the explosion, George Carey packed his camera and set off to Tunguska. He encountered a mixture of mystics, reindeer-herders, amateur sleuths and serious scientists and a range of theories, from meteorites and comets to alien spacecraft, anti-matter, spontaneous explosions and an unexpected passion for the Cosmos in the old Soviet Union. And on a lake near the epicentre, Carey witnesses a discovery that may finally reveal the truth.