In the 1980s, China's then-leader, Deng Xiaoping, had a vision of a megacity; 40 years on, it's one of the most futuristic metropolises in the world. In the first part of a three-part series, presenter Reggie Yates visits Shenzhen – former fishing village now home to 12.53m. In Huaqiangbei, the Silicon Valley of China, he meets two strikingly young inventors bringing science-fiction to life.