Southall's early books are stories of physical survival in the face of powerful natural forces. His later books, of which Josh is an outstanding example, show a change in direction. The theme shifts to the survival of the human spirit and personal integrity.

Southall's first three books following the Simon Black series—Hills End, Ash Road, and To the Wild Sky—have been referred to as his water, fire, and air trilogy. In Hills End, a group of children and their teacher, who have been exploring a cave in search of aboriginal cave paintings, return to find their small hometown flooded and deserted. The action of the story centers on their efforts to organize themselves to survive and rehabilitate their small town until outside help reaches them. In Ash Road, three boys on a camping trip accidentally start a huge brush fire that devastates...