Kate Croy, a young woman constrained by her impoverished circumstances, is drawn into the affluent world of her controlling Aunt Maud. While navigating the expectations imposed upon her, Kate becomes involved in a secret relationship with journalist Malcolm Densher, defying her aunt's ambitions for her to marry wealth.
Kate devises a plan to secure her future with Malcolm by manipulating the wealthy but terminally ill Milly Theale. Her growing closeness to Milly deepens her internal conflict as she balances love, ambition, and moral compromise.
As Milly's condition worsens, the consequences of Kate's scheme unravel. Malcolm is torn between his loyalty to Milly and his love for Kate, leading to a climactic resolution that questions the price of ambition and the nature of love.