Shortly after midday on December 17, 1967, Australia's Prime Minister Harold Holt made his way down to the beach for a swim. Onlookers said that as a large wave swept over, Holt seemed to disappear. Despite extensive air and sea searches, Holt's body was never found. After his disappearance, rumours circulated that Holt had been a spy, and had been taken away by a Chinese submarine. Could this be true?