A party is taking place at the house of Violetta Valery, a beautiful Parisian demimondaine. Gastone, a nobleman, arrives and presents his friend, Alfredo Germont, telling Violetta that Alfredo has long been a silent admirer and had called daily during her illness. Baron Douphol, Violetta’s current protector,  is angered by the conversation and refuses Gastone’s invitation to propose a toast. Alfredo accepts the invitation instead and sings an impassioned tribute to beauty and love. As the others go into another room to dance, Violetta suffers a fainting spell. Alfredo stays behind and confesses that he has been in love with her for a year. Violetta offers him friendship rather than love and gives him a flower, asking him to return when it has withered. Alfredo is overjoyed and bids her goodnight. When her guests leave, Violetta reflects on Alfredo’s proffered love, but finally decides that she must remain as she is, forever free to pass from pleasure to pleasure.

Some time later, Violetta and Alfredo are living a life of bliss in a country villa—at her expense..Alfredo finally realizes this and rushes off to Paris in order to borrow money from friends.
A visitor is announced to Violetta. It is Alfredo's father. He has come to free his son from the grasping and greedy clutches of this fallen woman. Violetta convinces Old Germont that the facts are quite different from his assumptions. She is supporting Alfredo, not the other way around, and the costs have nearly depleted her funds.
Old Germont is much moved, but then he explains that his daughter is about to marry a man of uptight nature. Germont believes that the wedding will not take place as long as his son is scandalously united with a notorious woman. Violetta is moved in her own way. In her life she has accepted much disgrace to get where she is. She cannot bring herself to do harm to a young girl who has a chance to live an entirely different sort of life. To spare the girl, she will give up Alfredo despite her love for him. Old Germont realizes her sacrifice and perhaps half-falls in love with her, himself.
Violetta receives a letter from her friend Flora. It is an invitation to a party. Violetta has given up Alfredo. She has no alternative but to return to her old life. She tearfully writes a letter of farewell to Alfredo before returning to Paris.
Alfredo returns. He finds the letter and the invitation. Violetta has betrayed him! She has returned to former life over the money she has spent on him. His outrage grows. His father attempts to calm him but Alfredo will have none of it. He will go to Paris to settle scores.