Hearing Jamie approaching the house, Tyrone steps into the next room. Jamie enters, drunk and slurring his speech. He drinks more, but he will not let Edmund drink at first, for health reasons. Jamie complains about Tyrone briefly, then learns of his agreement with Edmund. Jamie says that he spent the evening at the whorehouse, where he paid for a fat whore whom no one else was willing to take. Edmund attacks Jamie with a punch when Jamie begins praising himself and berating others. Jamie thanks him suddenly for straightening him out; he has been messed up by problems related to Mary's addiction. He and Edmund both begin to cry as they think about their mother. Jamie is also worried about Edmund, who may die from consumption. Jamie says that he loves Edmund, and that in a sense he made him what he is at present.
But Jamie also admits that he has been a bad influence, and he says that he did it on purpose. Jamie admits that he has always been jealous of Edmund, and he wanted Edmund to also fail. He set a bad example intentionally and tried to bring Edmund down. He then warns Edmund, saying, "I'll do my damnedest to make you fail," but then he admits, "You're all I've got left." Jamie then passes out.
Tyrone then reenters, having heard all that Jamie said. Tyrone says that he has been issuing the exact same warning to Edmund for many years. Tyrone calls Jamie a "waste." Jamie wakes up suddenly and argues with Tyrone. Jamie and Tyrone both pass out briefly until they are awoken by the sound of Mary playing the piano in the next room. The sound stops, and Mary appears. She is very pale and very clearly on a substantial dose of morphine. Jamie begins to cry, and Tyrone angrily cries that he will throw Jamie out of his house. Mary is hallucinating, thinking that she is back in her childhood. She thinks that she is in a convent. In her hands, she is holding her wedding gown, which she fished out of the attic earlier. She does not hear anyone, and she moves like a sleepwalker. Edmund suddenly tells Mary that he has consumption, but she tells him not to touch her because she wants to be a nun. The three men all pour themselves more alcohol, but before they can drink, Mary begins to speak. She tells them of her talk with Mother Elizabeth, who told her that she should experience life out of the convent before choosing to become a nun. Mary says that she followed that advice, went home to her parents, met and fell in love with James Tyrone, "and was so happy for a time." The boys sit motionless and Tyrone stirs in his chair as the play ends.
With Jamie's account of his evening in the city, we see that he perceives himself, like Holden Caulfield, to be a "catcher in the rye." Even though he is wasting his life away on whores and alcohol, he still feels a certain compulsion to help other people, and so he chooses to visit an obese prostitute who gets no customers. Jamie is willing to perform some self-sacrifice for the betterment of others, which is one of his stronger qualities. Although he tries to help the underdog, he is still willing to admit that he is not prepared to help his own brother. His confession to Edmund is remarkable for a kind of fatalistic maturity; he is willing to admit to his deep problems, even if he is not willing to try to solve them. In this case, Jamie may be better off than the other Tyrones, who have more difficulty admitting to their shortcomings. Right until the end of the play, for instance, Mary will never admit to her morphine addiction. Jamie, however, will confess fully to his abuse of his brother and the squandering of his own life.
If the play ends on a note of resolution, that resolution comes from confessing to faults in an attempt to better the future. Jamie, for instance, warns Edmund to watch out for his (Jamie's) jealousy, and before that, Tyrone acknowledges his own stinginess and agrees to send Edmund to a high-class sanatorium in hopes of curing him. Thus, two of the major family conflicts are at least partially resolved by the end of the play.
Of course, some problems are still left open, particularly Mary's morphine addiction, which we see at its worst in this act. Mary can no longer even see the real world as she falls into a hallucinogenic state in which she thinks she is back in her convent. It is very clear now that she takes her morphine to escape the reality of the present and to bring herself back to a time when her life was open and full of hope. Her closing speech ends the play with the expectation that the situation will not get better overnight. Instead, the play ends leaving the audience with the sense that the day is not particularly special; the events of this August day are likely to repeated by the family which is stuck in an endless cycle of broken dreams, conflicts and drugs.
Notice that, at the end of the play, O'Neill has created four complete characters with numerous strengths and weaknesses. One can clearly see some of both parents in each son, but one also sees the particular modifications that have taken place between the two generations. O'Neill does not end the play on any particular note of condemnation of any character. Rather, the play ends with an image of a resigned family that was once great but has since fallen into despair. Long Day's Journey into Night is undoubtedly a tragedy in its portrayal of this fallen family, but it is important to see that it does end offering some shreds of hope for the future if the characters can change the way they act and treat one another.