Lady Augusta Colebrook, "Gus," is determinedly unmarried, bored by society life, and tired of being dismissed at the age of forty-two. She and her twin sister, Julia, who is grieving her dead betrothed, need a distraction.

One soon presents itself: to rescue their friend's goddaughter, Caroline, from her violent husband. The sisters set out to Caroline's country estate with a plan, but their carriage is accosted by a highwayman. In the scuffle, Gus accidentally shoots and injures the ruffian, only to discover he is Lord Evan Belford, an acquaintance from their past who was charged with murder and exiled to Australia twenty years ago.

Gus needs Evan's help to rescue Caroline, and Evan needs Gus's help to clear his name. As they work together, solving a series of cases helping women in distress, they find themselves drawn to each other in ways neither expected.