Bertram, the count of Rossillion, is leaving his mother, the countess of Rossillion, to go with his companion, the evil-minded Parolles, to the court of France. He is under the guardianship of the king of France, who has for some time been seriously ill. Also saying goodbye to Bertram is Helena, the daughter of the late physician to the Rossillion family. She has been raised under the protection of the countess and is like a sister to Bertram, but she is also romantically in love with him. However, she realizes her chances of his love are slim because she was born into a lower class than he.
After Bertram leaves, Helena finally confesses her love to the countess, who encourages her. Thus, Helena follows Bertram to the French court, with plans to cure the king and win Bertram's hand.
When Helena arrives at the French court, the king does not fully trust her skill, despite his knowledge of her father's reputation. Thus, she makes a bargain with him: she will pledge her life that she can help him, and, if she is successful, she asks only that she be allowed to choose her own husband from the ranks of the eligible nobles of the court. Helena's cure, taken from her father's old books, is successful, and, when she is given her choice, she, of course, chooses Bertram. Other lords would have been glad to accept her beautiful hand, but not Bertram. He objects to the low social status of Helena and to the interruption of his young life. Nevertheless, the king, as Bertram's guardian and sovereign, insists that he accept Helena, so the marriage is performed.
But Bertram is not yet beaten. He runs away to the wars in Tuscany and sends Helena a letter telling her that until she can obtain his ancestral ring from his finger and have a child begotten by him, then and then only will he accept her as his wife-certainly an impossible task.
Helena, who has returned to Rossillion, then sets off disguised as a pilgrim. She arrives in Forence where she hears stories of the valor of Bertram and also of the licentious way in which Parolles leads his master into evil ways. A widow, who invites Helena to lodge at her house, tells how Bertram has been soliciting her own daughter, Diana, to be his mistress. Helena at this point has a plan and suggests that things be so arranged that Diana pretend to agree to Bertram's request, but Helena will herself take Diana's place in her bed in order to fulfill her husband's conditions and to save his virtue by tricking him into avoiding an illicit romance. The widow agrees, and Helena also has Diana obtain Bertram's ring before she agrees to the appointment. She tells the girl to promise Bertram that the ring will be replaced by another when they are in bed together.
Everything goes according to plan. Afterwards, Bertram unaware of the trick, returns to the camp. There he finds that his braggart-soldier friend, Parolles is to be tested for his courage. Of course, the windbag turns out to be an utter coward.
Helena, Diana, and the widow all return to France, where they go to the court and spread the rumor that Helena has died on her pilgrimage. Bertram soon hears the false news and believes he can now safely return to France, which he does. After he arrives, he proposes marriage to another woman, who asks that he give a ring as a betrothal token. He gives the ring that “Diana” had given him in bed, and the king immediately recognizes it as one that he himself had given to Helena. The king asks how Bertram obtained it, and, when the young man lies frantically, he accuses Bertram of having killed Helena. At that moment, a letter from Diana is brought in. She calls for justice since Bertram has not kept his promise to marry her. She then enters and tells her story, supported by her mother. Bertram tries to wiggle out of his difficulty and is saved only by the appearance of Helena (whose virtue he is now beginning to appreciate). Helena announces the fulfillment of all Bertram's conditions, and he now willingly accepts his wife. Diana is offered a large dowry and the promise of a suitable husband, the king and the countess are pleased with the outcome, and All's Well that Ends Well.