According to the Townsville Daily Bulletin, this was 'a story of a couple of daring thieves' attempt and their failure to steal an actress's black pearl necklace.'
The Sunday Times offers a slightly more detailed synopsis:
'The Mystery of the Black Pearl,' described as a thrilling story of crime and detection, will be presented for the first time. The plot deals with the robbery of a jewel, and, during the search for the criminals, many sensational incidents are portrayed. A well-known detective is bound and left to watch a tallow dip slowly burning in a keg of gunpowder, while just before the capture of "the gang" a fight in mid-air is presented.
Source:
'Australian Actors in Pictures', Sunday Times, 24 March 1912, p.2.