The Lithgow Plot was a purported assassination attempt of Queen Elizabeth II on 29 April 1970 at Lithgow, New South Wales, while she was undertaking a royal tour of Australia. The Queen and her husband were on a train trip from Sydney to Orange.
The would-be assassins supposedly rolled a large wooden log onto the tracks when it was dark and wedged it into place. According to retired Detective Superintendent Cliff McHardy, it was meant to de-rail the train and, if it did, it would have smashed into an embankment. It failed because, at the time, the train was travelling unusually slowly when it struck the blockage, though it still slid for 700 metres before coming to a stop.
A train had been through an hour before the Queen's train to check the line but at that time it was clear.
The royal couple were unaware of the attempt, and according to McHardy the government of Australia told the local police to keep quiet about the incident. This purportedly hampered the investigation attempt because people interviewed either couldn't or wouldn't speak about what had taken place.
In January 2009, McHardy gave the story to the Lithgow Mercury and The Daily Mail. Buckingham Palace declined comment on the issue but has said that diary of the trip has shown no record of the train hitting a log.