The Miracle Worker begins as a doctor reassures the parents of the infant Helen Keller that their daughter’s fever has passed; she will survive her severe illness. After the doctor leaves, the mother notices that the baby responds neither to hand movements in front of her eyes nor to any sounds. The anguished parents futilely call her name as the stage lights quickly dim.

When the lights rise, six-and-a-half-year-old Helen is playing with children who have cut out paper dolls. Attractive but unkempt and “noticeably blind,” with gestures that are “abrupt, insistent, [and] lacking in human restraint,” she is clearly undisciplined and often temperamental. She disrupts the group’s play, unknowingly using the scissors to menace her playmates’ eyes. Despite the family’s apparent strain, her mother remains patiently protective, and her father refuses to have Helen institutionalized, though she is thought to be mentally defective. Groping around the room, Helen knocks over furniture and cries until comforted by her mother. Trying to communicate, she makes only “an inarticulate weird noise in her throat such as an animal in a trap might make.” Nevertheless, there are some signs of intelligence: Realizing that her cloth doll lacks eyes, for example, she cleverly snatches buttons from her aunt’s dress to provide some. Although other doctors have failed, Keller agrees to write to a specialist in Boston.

In the next scene, the head of the Perkins Institute for the Blind prepares twenty-year-old Annie Sullivan for her new job as Helen Keller’s governess; herself partially sighted because of trachoma, Annie has been educated there. The younger schoolgirls present her with a doll for Helen and smoked eyeglasses for herself.

Arriving by train in Alabama, Annie is met by Mrs. Keller, who is astonished at the teacher’s youth. First, Annie says, she intends to teach Helen language— although, as she admits to her new pupil’s mother, no deaf-blind child has yet been taught even one-tenth of what an ordinary child learns.

At the homestead, Annie meets Helen and allows her to feel her hand, dress, and face. Together, they take her suitcase inside, where Annie allows her to open it with the key. Soon, she finds the elegant doll. Using the alphabet for the deaf, Annie signs the letters d-o-l-l into Helen’s palm, and her pupil imitates the gestures. When she takes the doll away, Helen becomes enraged, but Annie restrains her despite numerous slaps and kicks. Next, she teaches Helen the word c-a-k-e, but when Helen regains the doll she hits Annie’s face with it, drawing blood; she then rushes out of the room and locks Annie inside. That evening, Captain Keller rescues the teacher from the room, carrying her through a window and down a ladder into the yard, where Helen plays innocently beside the water pump while hiding the key inside her mouth. Later, Annie sees her drop the key down the well.

The second act opens with Annie reading aloud a letter she has written to the Perkins Institute; Helen must, she insists, first learn reasonable obedience. The next morning, Helen roams around the breakfast table, putting her hands into the food on others’ plates, as she is accustomed to do, but Annie refuses to allow her food to be groped. A violent tantrum ensues, but Annie will neither yield nor pity her as the Kellers have always done. Eventually, she asks them to leave and locks herself in the dining room alone with Helen, insisting that she sit at the table and eat her own food. A prolonged, wordless, extremely physical confrontation then occurs, during which Helen strikes Annie several times with her fists and is twice slapped in return.

When the day ends, Annie reports to the Kellers that their daughter has learned to sit at the table, eat with a spoon, and fold her napkin; Helen flees, however, whenever Annie comes near. That night, knowing that Captain Keller is outraged, Annie prepares to leave. He relents, offering her a second chance.

Contending that Helen’s worst handicap is the Kellers’ indulgent pity and overprotective love, Annie maintains that Helen must be made totally dependent on her alone and suggests that they live together elsewhere as long as necessary. She suggests moving into the Kellers’ garden house with Helen but making her think that they are far away. Her parents consent to a two-week trial period. After arriving at the garden house after a two-hour ride, Helen is enraged to find that her parents have gone, but late that night she takes renewed interest in learning words.

The third act takes place on the final day of the two-week period. Helen is neat, clean, well-mannered, obedient, and even able to crochet simple chains, but Annie is exhausted and frustrated. Though Helen knows the signs for twenty-one words, she does not yet associate words with things. Instead, she regards the signs as a meaningless finger-game that she can play even with the family dog. Annie begs the Kellers to grant her another week, hoping Helen will realize that “words can be her eyes, to everything in the world outside her, and inside too,” The Kellers insist, however, that Helen return home to them.

That evening, Helen deliberately tests her family’s indulgence, throwing her napkin on the floor repeatedly and beginning a tantrum when Annie removes her food. After her father orders it restored, she discards her fork, eats with her hands, tries to handle Annie’s food, and flings a pitcher of water at her. Annie then carries her, kicking and screaming, to refill the pitcher at the water pump in the yard. There, as Annie repeatedly spells w-a-t-e-r, the miracle happens: Helen associates the word and the thing, then joyously wants to know more words. The family is called to witness the change, and Helen learns to sign m-o-t-h-e-r and f-a-t-h-e-r for the first time. Next, Annie spells t-e-a-c-h-e-r and “I l-o-v-e H-e-l-e-n.”

Together, they enter the house, and the play ends.