The Williamsons live in a small mining town in Australia, and do the same as everybody do: dig and hope to find opals. Kellyanne (Sapphire), one of the family's two children, has little entertainment, but two very good although imaginary friends: Pobby and Dingan. One day Sapphire can no longer find her friends, and manages to make her none too thrilled father go look for them late at night. He is caught near his neighbor's mine diggings, and gets accused of stealing, or "ratting," a serious and much-hated crime in the town. This sets the stage for main part of the movie.

Opal Dream is based on the book Pobby and Dingan, which is praised for its touching, gentle quality. The movie is rather different, realistic and rough, with the largest merits perhaps in its depiction of the life style of the Australian opal miners and their community. Sapphire is very well fit for the role of a girl who ignores much of reality around herself, and lives for her imaginary friends; a little odd, not quite like everybody else, and completely charming enough that you'll feel for her loss.