Set in Canberra, Australia's capital city, Demonstrator concerns an Asian security conference organised by the government's Defence Minister, Joe Slater. Tension arises between Slater and his son Steven, who is leading a student protest against the conference. By the narrative's end, Steven has been beaten up, rejected by both his father and his girlfriend (Joe Slater's secretary), and seen what was to be a peaceful demonstration taken over by professional agitators.