Mathinna, an Aboriginal girl from Van Diemen's Land, is adopted by 19th-century explorer, Sir John Franklin, and his wife, Lady Jane. Franklin is confident that shining the light of reason on Mathinna will lift her out of savagery and desire. But when Franklin dies on an Arctic expedition, Lady Jane writes to Charles Dickens, asking him to defend Franklin's reputation amid rumours of his crew lapsing into cannibalism. Dickens responds by staging a play in which he takes the leading role as Franklin, his symbol of reason's triumph, only to fall in love with an 18-year-old actress. As reason gives way to wanting, the frontier between civilisation and barbarity dissolves, and Mathinna, now a teenage sex worker, goes drinking on a fatal night.
