Why does South Korea have the lowest fertility rate in the world? The average South Korean woman is expected to have 1.05 children in her life - exactly half the rate needed to maintain a population. That means a shrinking workforce paying less taxes and more elderly people who will need expensive care. South Korea's government has pumped tens of billions of pounds into dealing with the problem over the past decade, but the fertility rate is still going down. In this whodunnit, Simon Maybin finds out who's not doing it - and why.