Sophie can't walk or talk, but behind her disability hides a keen intelligence. Living on The Styx River cattle station with her father and a nanny, Sophie is acutely aware that she is a non-person. Sophie feels as voiceless and isolated as the wallabies of The Wall, an eerie wilderness of basalt lava tubes forming a natural stone labyrinth that protects its remote lushness from anyone foolish enough to wander in. Sophie's mother Rose, as The Wall's indigenous custodian, taught Sophie its secrets. When a bitter divorce forces Rose to leave, Sophie's father takes custody of both Sophie and The Wall. He and his "cronies" plot to build a multi-million dollar tourist resort, a development that will only go ahead if the rare wallabies are already extinct. But the cronies don't realise Sophie has heard their plans to hire roo shooters to help nature along. With the aid of computer technology, a desperate Sophie writes Silent Scream, an anonymous blog that reveals the threat. When scientists commissioned to find evidence of the wallabies' existence go missing, the rescuers appeal to Silent Scream for help. Raising awareness is one thing, but how can one impossibly disabled girl, who can barely help herself, help save the lives of others?