Anita Rani concludes her exploration the world of Indian cinema by examining how a new generation of Bollywood stars are challenging the industry to keep up with the country's unusually young population - more than half the 1.3 billion people in India are under 25. She also investigates why Indian cinema is so fascinated with having westerners on screen, and visits one of Asia's largest slums to find out about an increasing trend in Bollywood to use the enormous power of cinema to bring about social change.