In 1988, one of the most important television programmes in history was shown. Titled River Elegy, it was watched by perhaps 100 million Chinese viewers. Despite its stirring music and dramatic imagery, it wasn't a drama, or documentary - but an argument onscreen that China had been inward-looking and backward for too long, and had to turn to the west for renewal. It rejected the legacy of Mao's Cultural Revolution and daringly embraced the idea of learning from the empire across the "blue ocean" - the US. After Tiananmen Square in 1989, the show was banned and its makers went into exile. Yet it remains one of the rare examples of a broadcast that started a national conversation about modernisation and democracy - a dialogue abruptly cut off but perhaps not yet ended.