In early 20th century London, Kate Croy is a clever and ambitious young woman fighting against the constraints of her social position. Her life takes an unexpected turn when she meets Merton Densher, a passionate journalist with strong principles, with whom she begins an intense yet complicated romantic relationship. However, her dreams of a future together are threatened when Kate realizes that her aunt, with whom she lives, is willing to strip her of her inheritance if she does not marry a man of her social standing.
Desperate to secure her future, Kate devises a bold and morally questionable plan: she decides to interfere in the life of Millie Theale, a wealthy American heiress traveling to Europe in search of relief for her terminal illness. Kate convinces Merton to seduce Millie, not just for her fortune, but also so that she falls in love with him. As the plot unfolds, emotions begin to play a crucial role, and the lines between love, ambition, and sacrifice blur.
Things become more complicated when Merton starts to feel genuine affection for Millie, who, in turn, becomes an emotional support for Kate's insecurities. In a web of intrigue and passion, everyone becomes trapped in the consequences of their decisions, facing a dilemma that will change their lives forever.