Ruby Mills is ruthlessly ambitious, strikingly beautiful - and one of the Forty Thieves' most talented members. Harriet Littlemore writes the women's section in a local newspaper. She's from a 'good' London family and engaged to an up-and-coming Member of Parliament - but she wants a successful career of her own. After witnessing Ruby fleeing the scene of a robbery, Harriet develops a fascination with the elusive young thief that extends beyond journalistic interest. As their personal aspirations bring them into closer contact than society's rules usually allow, Ruby and Harriet's stories become increasingly intertwined. Their magnetic dynamic, fraught with envy and desire, tells a compulsive, cinematic story about class, morality and the cost of being an independent woman in 1920s London.