In Murder by Thirst, Sally Dunn, of Perth, Western Australia, was one of two students who traveled to London to complete their music studies at the London School of Music.
While on the flight from Darwin to London, Sally, and her partner John Murray had spotted Black Jack Barnes on the same flight. John and Sally's suspicions were aroused because Barnes, who had a bad reputation, had gone missing while out prospecting for gold in the Western Australian desert several weeks ago and had not been found after an extensive air search. Unable to account for Barnes' reappearance and the absence of his partner Mr Farlow, Sally and John decided that something was wrong. They speculated that Barnes might have murdered his partner and traveled to London to interest one of the large mining companies because he had found a gold strike too large for him to handle himself. Having read about Biggles, John and Sally decided to tell him about their suspicions. Biggles was impressed by their sound reasoning and decided to take up the case.