It is two years later than Act Three, a stormy night. Treplev has converted the parlor into a study for his writing. The Watchman taps his warning stick. Masha and Medvedenko enter the study, calling for Treplev using his nickname, "Kostya." Medvedenko and Masha discuss Sorin's request to see Treplev as Sorin's health fades fast. Medvedenko pleads with Masha to go home with him to feed their baby. Masha refuses, insisting that she will stay put for the night even though the baby has not seen his mother for two nights previous. Medvedenko criticizes the skeleton of a stage left over from Treplev's play that remains in the backyard. Masha does not mind its presence. Medvedenko complains that Masha's father Shamrayev will not lend him a horse to take home if Masha does not go home too. She tells Medvedenko to ask him anyway. Masha is troubled about Sorin's condition and frustrated by Medvedenko's pestering.
Paulina and Treplev enter with bed linens, pillows, and a quilt for Sorin who wants to sleep in Treplev's study. Masha makes a bed for Sorin on the divan. Medvedenko says goodbye to everyone, but no one really cares that he is leaving. Paulina looks over Treplev's shoulder at his writing. She comments that no one thought Treplev would become a genuine writer but now he is making money writing and looks handsome. She asks Treplev to pay some attention to Masha. Paulina explains that it would mean a lot to Masha because women appreciate compliments more than men realize. Paulina adds that she feels the same way, saying, "Believe me, I know." Masha is embarrassed and asks her mother to leave Treplev alone.
Treplev leaves the room. Masha blames Paulina for his exit. Paulina says that she feels sorry for Masha and her unrequited love for Treplev. Masha tells her mother that Medvedenko has been offered a teaching job in another district and they will move away in a month. Masha tries to convince Paulina that none of her hurt feelings about Treplev matter because she will soon forget.
Medvedenko and Dorn enter pushing Sorin in on a wheelchair. Masha asks Medvedenko why he has not left yet. He tells her that her father would not lend him a horse. Medvedenko complains to Dorn about his lack of finances with self- pity, suggesting that Dorn would not understand because he has lots of money. Dorn fires back a rebuttal to Medvedenko's accusation, saying that he worked as a doctor for thirty years without a vacation and was constantly on call. The Watchman taps his warning stick.
Sorin asks for Arkadina, but she is out picking up Trigorin from the train station. Sorin comments that if his sister has been sent for, then he must be close to death. He announces that he has an idea for a short story for Treplev to write called, "The Man who Wanted." It would reflect Sorin's attitude about his own life in which, he feels, he never achieved the things he once hoped to accomplish such as becoming a writer and eloquent speaker. Dorn tells him that at his age it is late to waste time having regrets.
Medvedenko asks Dorn which city he traveled to that he liked the best. Dorn replies that he like Genoa the best because of "the crowd in the streets" and the constant flow of people. This reminds Dorn of Treplev's play and the phrase, "I am the universal soul." Dorn asks Treplev about Nina's life now. Treplev tells Dorn that Nina had an affair with Trigorin, became pregnant, the baby died and Trigorin left her for Arkadina whom he was with while he impregnated Nina, cheating on them both.