Is Harold Holt still alive? Did he commit suicide? Was he drunk or drugged? Did he secretly belong to a crime syndicate? Was he a Chinese Communist spy?

With the media and others battling to comprehend how someone could simply disappear, the void was filled with numerous allegations, rumours, insinuations and conspiracy theories.

The 'Chinese spy theory' was suggested by Ronald Titcombe and appeared in Anthony Grey’s book, The Prime Minister Was a Spy (1983). The claim was that Holt had been spying for the Communists for 30 years and was spirited away by scuba divers to a Chinese submarine waiting offshore. The book made headlines around the world and is a theory that many Australians remember, even if they don't take it seriously.

This clip is from the documentary, The Harold Holt Mystery (Ten Network, 1985).