Alceste, a French aristocrat, raves to his friend Philinte about the corruption of French society. Alceste identifies hypocrisy as one of mankind's worst flaws. Despite Philinte's objections, Alceste insists that truth and honesty, no matter how painful, are essential to true integrity. Philinte contends that honesty must be balanced with manners, arguing that flattery might justly take the place of offensiveness. He believes that human nature should be allowed its faults. Over the course of the conversation, we learn that Alceste is presently involved in a lawsuit.
During the conversation between Alceste and Philinte, Oronte, a marquis of the Court enters, proposing that he and Alceste commit to being friends. Alceste makes no such commitment, suggesting that they get to know each other first. Shortly thereafter, Oronte asks Alceste to critique a sonnet he has written. Alceste reluctantly agrees. He despises the poem, and scolds Philinte for flattering Oronte. When Oronte asks Alceste's opinion, Alceste suggests that Oronte give up his aspirations as a poet. Insulted, Oronte leaves.
Alceste confronts his love interest Célimène (whose house is the setting for the play) about her recent behavior, which he considers inappropriate. He criticizes her for entertaining too many suitors; she insists that her flirtation is harmless and that her true affections lie with him. Célimène's manservant, Basque, announces the arrivals of Acaste and Clitandre, two marquises hoping to court Célimène. In protest, Alceste announces that he will leave, but he does not.
All of Célimène's suitors, excluding Alceste, gather with her and her female cousin, Éliante, to hear Célimène's gossip about the people of the Court. Célimène criticizes harshly, and her suitors are highly entertained. Alceste interjects during Célimène's discussions to object to the hypocrisy at hand. Everyone dismisses his comments. Éliante delivers her ideas about men in love, mentioning that Alceste's disposition is abnormal. She contends that smitten men typically compliment those with whom they are in love.
An Officer of the Marshals of France arrives to inform Alceste that a lawsuit has been filed against him by Oronte, who seeks retribution for Alceste's comments about his poem. Alceste leaves to deal with the matter.
Acaste and Clitandre find a moment alone to discuss their affections for Célimène. Acaste strokes his own ego, bragging about his youth, his wealth, and his appeal to women. His cheerfulness dissolves, however, when he admits that Célimène does not care for him. Clitandre and Acaste decide that, should one of them fall out of favor with Célimène for good, he will step aside and support the other's courtship.
Arsinoé, a cantankerous older woman, arrives to tell Célimène that the people of the court have been talking about her "flirtatiousness." Arsinoé claims to have taken Célimène's side in the affair, but she suggests that Célimène change her behavior promptly to avoid further conflict. Célimène comments on Arsinoé's flaws, implying that Arsinoé's pretentiousness is also a topic of conversation. Arsinoé takes offense when Célimène states that the older woman's flaws might just be the result of age.
The dispute ends when Alceste arrives, at which point Célimène leaves. Arsinoé praises Alceste's integrity and offers to use her influence to acquire him a position at Court. He scoffs at her offer. She then tells Alceste that she has a letter proving Célimène's deception of him. Alceste leaves with Arsinoé to see the evidence for himself.
Philinte and Éliante discuss Alceste's extraordinarily foul behavior before the Marshals of France. Philinte can hardly believe Alceste's unwillingness to compromise, while Éliante praises Alceste's commitment to his own value system. When their conversation turns to Alceste's relationship with Célimène, Éliante states that Célimène is confused and does not know whom she loves. Éliante admits that she would accept Alceste's advances if he were to abandon Célimène at any point. Philinte then admits his attraction to Éliante, saying he would be honored to be hers.
As Philinte and Éliante finish their conversation, Alceste enters, infuriated and seeking revenge against Célimène for deceiving him by professing her attraction to another suitor. Alceste proposes that he and Éliante strike up a relationship in order to make Célimène jealous. Éliante cautions Alceste not to be hasty in his judgment.
Philinte and Éliante exit as Célimène enters. Alceste berates Célimène for her infidelity. She reacts calmly, calling him "foolish" and telling him to believe what he wishes about the letter. Desperate, Alceste commands Célimène to tell him that the letter was actually written to a woman. Célimène refuses this request, and Alceste rages about his uncontrollable love for her.
Alceste's servant, Du Bois, enters, telling his master to leave immediately, as he has lost his court battle and now runs the risk of arrest. Alceste leaves to find out more about the situation. He finds Philinte, who counsels him to challenge the verdict issued against him. Alceste refuses, stating that he wants the verdict to stand as an example of human corruption. He announces that he will isolate himself from society forever. Before leaving, he plans to test Célimène's love by asking her to retire with him.
Shortly thereafter, Alceste and Oronte confront Célimène, both demanding that she choose between them. Célimène refuses to do so, stating that she plans to let Éliante make the decision for her. When Éliante enters, she refuses to do Célimène's bidding. Then, Acaste and Clitandre enter with a letter written by Célimène that contains insulting remarks about each of the suitors. Arsinoé and Philinte return. The men read the letter aloud, each of them declaring his wish to end whatever courtship he had with Célimène.
Eventually, Alceste is the only suitor remaining. For once, he is willing to forgive Célimène, but he says she must first agree to live with him in solitude. She is shocked by his proposal, explaining to him that she is too young to make such a drastic decision. She agrees to marry him, but not to leave with him. Furious, Alceste renounces his love for Célimène. She leaves, and Alceste turns to Éliante, telling her that it would be unjust for him to ask for her devotion. Éliante professes agreement, announcing her decision to devote herself to Philinte. Alceste exits, and Philinte and Éliante follow to encourage him to rethink his decision to retire into isolation.