The play takes place in London. On a summer evening, rain pours out of the bucket. Passers-by run to the Covent Garden Market and to the portico of St. Pavel, where several people have already taken refuge, including an elderly lady with her daughter, they are in evening dresses, waiting for Freddie, the lady’s son, to find a taxi and come for them. All but one person with a notebook look eagerly into the streams of rain. Freddie appears in the distance, not finding a taxi, and runs to the portico, but on the way he lands on a street flower girl, rushing to hide from the rain, and knocks out a basket of violets from her hands. She bursts into abuse. A man with a notebook writes something in a hurry. The girl laments that her violets have disappeared, and begs the colonel who is standing right there to buy a bouquet. That, to get rid of, gives her a trifle, but does not take flowers. One of the passersby draws the attention of the flower girl, a sloppy dressed and unwashed girl, that a person with a notebook is clearly scribbling at her. The girl begins to whimper. He, however, assures that he is not from the police, and surprises everyone present by precisely determining the origin of each of them by their pronunciation.

Freddy's mother sends her son back to look for a taxi. Soon, however, the rain stops, and she and her daughter go to the bus stop. The colonel is interested in the abilities of a person with a notebook. He introduces himself as Henry Higgins, creator of the Universal Higgins Alphabet. The colonel is the author of the book "Conversational Sanskrit." Surname is his pickering. He lived in India for a long time and came to London specifically to meet Professor Higgins. The professor also always wanted to meet the colonel. They are about to go to dinner with the colonel at the hotel when the flower girl again begins to ask her to buy flowers. Higgins throws a handful of coins into her basket and leaves with the colonel. The flower girl sees that she now owns, by her standards, a huge amount. When Freddy arrives with a taxi he finally caught, she gets in the car and, shutting the door shut with a noise, leaves.

The next morning, Higgins shows Colonel Pickering his phonographic equipment at home. Suddenly, Higgins' housekeeper, Mrs. Pearce, reports that a very simple girl wants to speak with the professor. Yesterday's flower girl enters. She introduces herself as Eliza Dolittle and says that she wants to take phonetics lessons from the professor, because with her pronunciation she cannot get a job. The day before, she heard Higgins give such lessons. Eliza is sure that he will gladly agree to work out the money that he threw into her basket yesterday without looking. Talking about such amounts, of course, is ridiculous to him, but Pickering offers a bet to Higgins. He encourages him to prove that in a matter of months he can, as he assured the day before, turn a street flower girl into a duchess. Higgins finds this offer tempting, especially since Pickering is ready, if Higgins wins, to pay the full cost of Eliza's tuition. Mrs. Pierce leads Elisa to the bathroom.

After some time, Eliza's father comes to Higgins. He is a garbage man, a simple man, but he impresses the professor with his natural eloquence. Higgins asks Doolittle for permission to keep his daughter at home and gives him five pounds for it. When Eliza appears, already washed in a Japanese bathrobe, the father at first does not even recognize his daughter. After a couple of months, Higgins brings Eliza to her mother’s house, just on her foster day. He wants to know whether it is already possible to introduce a girl to secular society. Mrs. Higgins is visiting Mrs. Ainsford Hill with her daughter and son. These are the very people with whom Higgins stood under the portico of the cathedral on the day when he first saw Eliza. However, they will not recognize the girl. At first, Eliza behaves and talks like a high-born lady, and then she goes on to talk about her life and uses street expressions such that all those present are only amazed. Higgins pretends that this is a new secular jargon, thus smoothing the situation. Eliza leaves the crowd, leaving Freddie in complete delight.

After this meeting, he begins to send Eliza letters in ten pages. After the guests leave, Higgins and Pickering vying with each other, enthusiastically tell Mrs. Higgins about how they deal with Eliza, how they teach her, take her to the opera, to exhibitions, and dress. Mrs. Higgins finds that they treat the girl like a living doll. She agrees with Mrs. Pierce, who believes that they are “not thinking about anything.”

A few months later, both experimenters took Eliza to a grand reception, where she was a dizzying success, everyone took her for the Duchess. Higgins wins the bet.

Arriving home, he enjoys the fact that the experiment, from which he had already managed to get tired, is finally over. He behaves and speaks in his usual rude manner, without paying the slightest attention to Eliza. The girl looks very tired and sad, but at the same time she is dazzlingly beautiful. It is noticeable that irritation accumulates in it.

In the end, she runs into Higgins with his shoes. She wants to die. She does not know what will happen to her next, how to live. After all, she became a completely different person. Higgins assures that everything will be fine. She, however, manages to offend him, unbalance, and thereby avenge herself at least a little.

At night, Eliza runs away from home. The next morning, Higgins and Pickering lose their heads when they see that Eliza is gone. They even try to find her with the help of the police. Higgins feels without Eliza as without arms. He does not know where his belongings are, nor what things are assigned to him on the day. Mrs. Higgins arrives. Then they report on the arrival of father Eliza. Dolittle has changed a lot. Now he looks like a prosperous bourgeois. In indignation, he attacks Higgins because of his fault he had to change his lifestyle and now become much less free than he was before. It turns out a few months ago, Higgins wrote to America to one millionaire, who founded branches of the League of Moral Reforms around the world, that Doolittle, a simple scavenger, is now the most original moralist in all of England. He died, and before his death, he bequeathed to Doolittle a share in his trust for three thousand annual income, provided that Doolittle would give up to six lectures a year in his League of Moral Reforms. He laments that today, for example, he even has to officially marry the one with whom he had lived without a relationship for several years. And all this is because he is now forced to look like a respectable bourgeois. Mrs. Higgins is very glad that the father can finally take care of his changed daughter, as she deserves. Higgins, however, does not want to hear about “returning” to Doolittle Eliza.

Mrs. Higgins says she knows where Eliza is. The girl agrees to return if Higgins asks her for forgiveness. Higgins in no way agrees to go for it. Eliza enters. She expresses gratitude to Pickering for his treatment of her as a noble lady. It was he who helped Eliza change, despite the fact that she had to live in the house of a rude, sloppy and ill-bred Higgins. Higgins is amazed. Eliza adds that if he continues to “crush” her, she will go to Professor Nepin, Higgins' colleague, and will become his assistant and will inform him of all the discoveries made by Higgins. After a surge of indignation, the professor finds that now her behavior is even better and more worthy than when she watched his things and brought him slippers. Now, he is sure, they will be able to live together not just as two men and one stupid girl, but as "three friendly old bachelors."

Eliza goes to her father’s wedding. Apparently, she still will live in Higgins' house, because she managed to become attached to him, like him to her, and everything will go on with them as before.