In Australia, eight men swindle a mine and ranch owner named Mrs. Cartier out of all she possesses. Shocked by her losses, the woman collapses and dies. Her daughter, Mademoiselle Yvonne, realises that a swindle has occurred and vows revenge on the men.
Sexton Blake gets involved much later in the story, initially protecting one of the villains. Yvonne proves, even to Blake, to be a formidable foe.
This is the first of a series of 'Mademoiselle Yvonne' stories.