Act I
Olga (the eldest sister) has worked as a schoolteacher and after school tutor for four years. Masha, middle sister and artist of the family (trained as a concert pianist), is married to Feodor Kulygin, a schoolteacher. Masha, younger than he, was enchanted by his wisdom but seven years later she sees through his pedantry and attempts to compensate for the emptiness between them. Irina, the youngest sister, is still full of expectation, speaking of going to Moscow and meeting her true love. The sisters grew up in Moscow, and they all long to return to the happiness of that time. Andrei is the only young man in the family; his sisters adore him. He falls in love with Natalia Ivanovna ("Natasha"), who is rather "common" compared to the sisters and regarded by them with disdain. The play begins on the first anniversary of the death of their father, Sergei Prozorov. It is also Irina's name-day, and everyone, including the soldiers (led by Vershinin) bringing with them a sense of noble idealism, come together to celebrate it. At the close of the act, Andrei confesses his feelings to Natasha, and proposes.
Act II
Almost a year later, Andrei and Natasha are married with their baby (offstage), a son named Bobik. Natasha is having an affair with Protopopov, Andrei's superior, who is never seen onstage. Masha comes home flushed from a night out, and it is clear that she and her companion, Lieutenant-Colonel Vershinin, are giddy with their mutual love for one another. Natasha manipulatively quashes the plans for a party in the home; the resultant quiet suggests that happiness is being quashed as well. Tuzenbach and Solyony both declare their love for Irina.
Act III
About a year later in Olga and Irina's room—a clear sign that Natasha is taking over the household, as she asked them to share a room so that Bobik could have a separate room. There has been a fire in the town, and people are passing in and out, carrying materials to give aid. Olga, Masha and Irina are angry with Andrei for mortgaging their home without their knowledge or consent, keeping the money to pay off his gambling debts and ceding all power over the household to Natasha. Natasha is cruel to the aged family retainer, Anfisa, but Olga's best efforts to counter this fail. Masha, alone with her sisters, tells them of her romance with Vershinin. At one point, Kulygin blunders into the room, doting foolishly on Masha, and she leaves. Irina despairs at the turn her life has taken, the life of a municipal worker, and rails at the folly of her aspirations. Supported by Olga's realistic outlook, Irina decides to accept Tuzenbach's offer of marriage although she does not love him. Andrei vents his self-hatred, acknowledges his awareness of his folly and his disappointment in Natasha, and begs his sisters' forgiveness for everything.
Act IV
The soldiers are preparing to leave the area. A photograph is taken. There is tension because Solyony has challenged Tuzenbach to a duel. Solyony had told Irina that he would kill any successful suitor for her hand, but she still agreed to marry Tuzenbach, notwithstanding which she confesses that she cannot love him. Tuzenbach, having left the Army, is under no obligation to agree to the duel but does so anyway, losing his life for what would have been a loveless marriage. As the soldiers are leaving, a shot is heard, and Tuzenbach's death in the duel is announced shortly before the end of the play.
Masha has to be pulled, sobbing, from Vershinin's arms, but her husband compassionately asks that they start again. Olga has reluctantly accepted the position of permanent headmistress of the school where she teaches and is moving out. She is taking Anfisa with her, rescuing the elderly woman from Natasha.
Irina's fate is uncertain but, even in her grief at Tuzenbach's death, she wants to persevere as a teacher. Natasha remains as the chatelaine, in charge of everything. Andrei is stuck in his marriage with two children, unwilling and unable to do anything for his wife or himself. As the play closes, the three sisters stand in a desperate embrace, gazing off as the soldiers depart to the sound of marching music. As Chebutykin sings Ta-ra-ra-boom-di-ay to himself,[nb 1] Olga's final lines seek an end to the confusion the sisters feel at life's sufferings and joy: "If we only knew... If we only knew."
