It is midnight. Tyrone, drunk, sits at a table playing solitaire as Edmund returns. They immediately argue about Edmund's having left the hall light on. Tyrone is worried about the cost, but Edmund calls him a cheap skate to worry about just one bulb. Tyrone threatens to hit him if he does not turn the light out, but then feels guilty as he remembers how ill his son is. He apologizes, as does Edmund. Edmund offers to turn the light out, but Tyrone tells him to leave it on. He even lights the three bulbs in the chandelier, but as he does so he lets on that he fears that his life will end in poverty.
He asks where Jamie is, and when Edmund says he does not know, Tyrone assumes he is at a brothel. As the two men share a drink, Edmund recites a poem and says he enjoyed walking home in the fog. Everything seemed unreal and it was as if he had escaped from the truth of life. Tyrone is impressed at the poetic nature of Edmund's words, but he thinks his son is morbid. He thinks that Shakespeare is the greatest poet and all the rest are third-rate. Edmund recites a poem by the French symbolist poet Baudelaire, but Tyrone thinks that is morbid too, although he compliments his son on his recital. Edmund recites another Baudelaire poem, saying that it describes the kind of life Jamie leads. Tyrone denounces it as morbid filth. He assumes Baudelaire was an atheist. He then attacks Edmund's taste in literature, indicating a small bookcase at the rear: Voltaire, Rousseau, Schopenhauer, Nietzsche and Ibsen were all atheists, fools and madmen. Poets such as Baudelaire, Swinburne, Wilde, Whitman and Poe were "whoremongers and degenerates." He hates Zola and Dante Gabriel Rossetti too. None of them can compare to Shakespeare. Edmund responds that he knows Shakespeare too, recalling that he once won a bet from his father for learning the part of Macbeth in a week. They drink more and there is a good feeling between them. Tyrone talks resentfully about Mary and the past, saying that the wonderful home she said she grew up in was in fact rather ordinary. Her father was prosperous, but he took to drink and died of consumption.
They decide to play a card game. They can't go to bed until Jamie returns, and neither wants to go upstairs until Mary is asleep. Tyrone, still thinking about Mary, says that her dream of becoming a concert pianist was put into her head by the nuns, who flattered her because she was so devout. He also says she never had any ambition to be a nun; she had too much love of the world ever to renounce it.
As they continue to play cards, Tyrone mentions how frightened his wife is regarding Edmund's illness, and she is not responsible for what she says when the poison (the morphine) gets hold of her. Edmund reacts angrily, blaming his father for her addiction, because he would not pay for a good doctor when Mary was ill after giving birth to Edmund. Tyrone protests that the doctor had a good reputation, but Edmund is not mollified. He attacks his father for not sending Mary away for a cure because that would have involved spending money. Tyrone defends himself, saying it was years before he knew what was wrong with her. He says he has spent thousands on cures, but none of them ever work. Edmund remains angry, saying that Tyrone has never given Mary any reason to want to stay off drugs, failing to provide her with a decent home and dragging her along with him to his acting engagements, season after season, staying in cheap hotels with no one to talk to. Tyrone responds that she wanted to travel with him, and there were always members of the acting company that she could have talked to.
The argument peters out, and they are affectionate toward each other again. But anger soon flares up again, and Edmund attacks his father for sending him to a state sanatorium just to save money. He says he will refuse to go. Tyrone protests that he will send Edmund anywhere that Edmund wants. He doesn't care what it costs. He then confesses that his attitude to money is shaped by fear of ending up in poverty. That's why he has always tried to buy land, since that makes him feel more safe financially. He points out that Edmund had a comfortable childhood, with nurses, schools and college, even though he did not finish college. He contrasts that with his own impoverished childhood. When he was ten his father deserted his mother and went back to Ireland, where he soon died. His mother was left to raise four small children. Twice they were evicted from their home. At the age of ten Tyrone worked twelve hours a day in a machine shop, in dark, dirty conditions. But they were always extremely poor. It was then that he learned to be a miser. He returns to the topic of the sanatorium, saying that he will send Edmund to any place he wants to go, no matter what it costs-within reason. He mentions a sanatorium the specialist recommended, endowed by a group of millionaire factory owners. It is also inexpensive. Edmund, no longer resentful, agrees to go there.
Tyrone then reminisces about his career. He had once had great talent and was considered one of the most promising actors in America. He loved Shakespeare, and the great actor Edwin Booth complimented him on his performance as Othello, saying that it was better than he ever did. Tyrone was then twenty-seven years old, but that turned out to be the high point of his career. After he married Mary, he was offered a part in a popular play that was a huge box office success. He made a lot of money from it, but became stereotyped in the role, so he was offered no other roles. He lost his early talent through never having to learn a new role.
Edmund expresses his appreciation that his father has shared his story with him, and then shares his own memories about the time he spent as a sailor. On several occasions when he was at sea, he had moments of complete peace and freedom, when he felt at one with nature. For those brief moments everything made sense to him, there was meaning in life, as if a secret had been disclosed. But then it was gone and he was stumbling in the fog again. Tyrone tells him that he has the makings of a poet, but Edmund says regretfully that he does not have the ability.
They hear Jamie returning. Tyrone knows that Jamie must be drunk, and fears that he will lose his temper with his son, so he goes out on the porch.
Jamie enters, noisily drunk, and helps himself to another drink of whiskey. Edmund wants a drink too, but Jamie tries to stop him because the doctor told him not to drink. Jamie says he loves his kid brother and does not want to lose him. But Edmund does not listen and pours a drink. Jamie starts abusing his father as a miser, letting on to Edmund that Dr. Hardy had told him the sanatorium Tyrone was sending him to was a "charity dump." Edmund explains that their father now says he can go anywhere he wants, but Jamie sneers at the "within reason" clause. He then tells Edmund about the evening he spent at Mamie Burns's brothel with a prostitute named Fat Violet. But his amused tone changes after a while as he realizes the degradation into which he has sunk. He knows that his life is a failure.
Jamie then makes a cruel remark about his mother, referring to her as a "hophead." Edmund is so incensed he punches Jamie in the face. Jamie is penitent, and Edmund apologizes. Jamie explains his disappointment with his mother. He thought she had beaten the addiction, and this gave him hope that he might beat his. But now he knows that she has not recovered after all. Jamie then rambles resentfully about drug addiction and Edmund's consumption. He sneers at Edmund as an overgrown kid who is his mother's baby and his father's pet. He also sneers at Edmund's poems that have been published in the local newspaper. Then he regrets his words and tells Edmund he is proud of his achievements. He even wants to take credit for them himself, since he has had more influence on Edmund's upbringing than anyone else. But then, as he continues to drink, his tone changes again. He admits that he has been a bad influence on his brother, but worse, he did it on purpose. He did not want Edmund to succeed, because that would make him, Jamie, look worse by comparison. He was always jealous of Edmund. But then he says he loves him more than he hates him, and he hopes he does succeed. But he also warns him, that if he does, he better be on his guard, because he, Jamie, will try his hardest to make him fail.
Jamie falls into a drunken doze, and Tyrone returns from the porch. He has heard part of what Jamie said, and tells Edmund that he hopes he heeds the warning, but then he adds that Jamie exaggerates. He is really devoted to Edmund. Tyrone looks down at Jamie with sadness, regretting the wasted life of his son.
Jamie emerges from his stupor, and argues with his father. But they are both too sleepy to continue it for long.
Mary comes down from upstairs and sits at the piano in the front parlor and plays a simple Chopin waltz. She then appears in the doorway in her dressing gown. Her eyes look enormous but her face is paler than ever. Over one arm, she carries a white satin wedding dress. The three men stare at her but she seems unaware of them. Jamie makes a mocking remark and Edmund slaps him across the mouth. Jamie accepts that he had it coming and starts to sob. Tyrone threatens to throw him out of the house the next day.
Then Mary begins to speak, aloud to herself. She talks as if she is back in the convent as a girl, saying she is out of practice and playing badly. She examines her swollen hands with puzzlement, and says she must go to the infirmary and show them to Sister Martha. As she comes into the room, Tyrone takes the wedding gown from her. She thanks him without appearing to recognize him. She tries to remember what she has come down for; she knows she has lost something. Tyrone tries to speak to her but Jamie tells him it is hopeless. Edmund tells her she has consumption, and for a second it appears as if he has got through to her. But then she retreats into her own world of childhood again. Tyrone says it is no use trying to reach her. He pours himself a drink and passes the bottle to the others. Mary goes on talking, oblivious of their presence. She says she had a talk with Mother Elizabeth and told her she wanted to become a nun. Mother Elizabeth told her to go home after she graduated and live as other girls lived. Then if after a year or two she still felt sure she wanted to be a nun, she should come back and they would talk about it. Mary says she was shocked at this advice. The following spring, she fell in love with James Tyrone and was happy for a time.
The curtain comes down as Mary stares ahead.
The final Act is structured in three sections: Tyrone and Edmund's argument that leads to some measure of mutual understanding; Edmund and Jamie's interaction in which the emphasis is on Jamie's self-knowledge and his feelings for his brother; and Mary's descent into a fantasy world of her girlhood, which the men merely observe.
The scene between Tyrone and Edmund begins, not unexpectedly, with an argument, and Tyrone's miserliness almost leads to physical violence when Edmund refuses to turn the light out. The continuing argument is as vicious a quarrel as any in the play, with Edmund at one point declaring that when he thinks of how Tyrone treated Mary, he hates his father's guts. But eventually the two men learn to listen to each other, and they gain a mutual understanding that had eluded them before. This begins when Tyrone recalls the hardships he endured growing up. He admits that he is a miser and explains how it came about. He talks candidly about how he ruined his career because he was seduced by the lure of financial success. He drops all his pride and pretense as he tells the story, and it is this honesty that impresses and moves Edmund. He feels he is getting to know his father better. It is as if the mask that his father wears all the time (he is, after all, an actor) has finally been discarded. This prompts Edmund to respond by revealing himself, particularly his love of poetry, more fully in this Act than he has done up to now. His father listens and is impressed, even though he finds some of the sentiments Edmund expresses to be morbid. Their conversation is broken off by the drunken entry of Jamie, but these moments of mutual respect are moving. Understanding between father and son comes haltingly, is incomplete, and can never be enough to overcome the pain of the past, but it is at least a step in the right direction.
In the second section of the Act, Jamie reveals a self-understanding that he has not expressed up to this point, and he is searingly honest about his love-hate feelings for Edmund. The truth may be hard, but at least in this final Act of the Tyrone family's long journey into night, it is coming out.
The final section of the Act contrasts with the earlier two. Whereas Tyrone, Edmund and Jamie all learn to face the truth, to a greater or lesser degree, Mary slips further and further into illusion.