The scene opens as usual on the living room at 6:30 pm, just before dinner time. Mary and Cathleen are alone in the room; Cathleen, at Mary's invitation, has been drinking. Although they discuss the fog, it is clear that Cathleen is there only to give Mary a chance to talk to someone. They discuss briefly Tyrone obsession with money, and then Mary refuses to admit to Edmund's consumption. Mary delves into her past memories of her life and family. As a pious Catholic schoolgirl, she says that she never liked the theater; she did not feel "at home" with the theater crowd. Mary then brings up the subject of morphine, which we learn Cathleen gets for her from the local drugstore. Mary is becoming obsessed with her hands, which used to be long and beautiful but have since deteriorated. She mentions that she used to have two dreams: to become a nun and to become a famous professional pianist. These dreams evaporated, however, when she met Tyrone and fell in love. She met Tyrone after seeing him in a play. He was friends with her father, who introduced the two. And she maintains that Tyrone is a good man; in 36 years of marriage, he has had not one extramarital scandal.
Cathleen then exits to see about dinner, and Mary slowly becomes bitter as she recalls more memories. She thinks of her happiness before meeting Tyrone. She thinks that she cannot pray anymore because the Virgin will not listen to a dope fiend. She decides to go upstairs to get more drugs, but before she can do so, Edmund and Tyrone return.
They immediately recognize upon seeing her that she has taken a large dose of morphine. Mary tells them that she is surprised they returned, since it is "more cheerful" uptown. The men are clearly drunk, and in fact Jamie is still uptown seeing whores and drinking. Mary says that Jamie is a "hopeless failure" and warns that he will drag down Edmund with him out of jealousy. Mary talks more about the bad memories from the past, and Tyrone laments that he even bothered to come home to his dope addict of a wife. Tyrone decides to pay no attention to her. Mary meanwhile waxes about Jamie, who she thinks was very smart until he started drinking. Mary blames Jamie's drinking on Tyrone, calling the Irish stupid drunks, a comment which Tyrone ignores.
Mary's tone suddenly changes as she reminisces about meeting Tyrone. Tyrone then begins to cry as he thinks back on the memories, and he tells his wife that he loves her. Mary responds, "I love you dear, in spite of everything." But she regrets marrying him because he drinks so much. Mary says she will not forget, but she will try to forgive. She mentions that she was spoiled terribly by her father, and that spoiling made her a bad wife. Tyrone takes a drink, but seeing the bottle has been watered down by his sons trying to fool him into believing that they haven't been drinking, he goes to get a new one. Mary again calls him stingy, but she excuses him to Edmund, telling of how he was abandoned by his father and forced to work at age 10.
Edmund then tells Mary that he has tuberculosis, and Mary immediately begins discrediting Doc Hardy. She will not believe it, and she does not want Edmund to go to a sanatorium. She thinks that Edmund is just blowing things out of the water in an effort to get more attention. Edmund reminds Mary that her own father died of tuberculosis, then comments that it is difficult having a "dope fiend for a mother." He exits, laving Mary alone. She says aloud that she needs more morphine, and she admits that she secretly hopes to overdose and die, but she cannot intentionally do so because the Virgin could never forgive suicide. Tyrone reenters with more whiskey, noting that Jamie could not pick the lock to his liquor cabinet. Mary suddenly bursts out that Edmund will die, but Tyrone assures her that he will be cured in six months. Mary thinks that Edmund hated her because she is a dope fiend. Tyrone comforts her, and Mary once again blames herself for giving birth. Cathleen announces dinner. Mary says she is not hungry and goes to bed. Tyrone knows that she is really going for more drugs.
Notice that, as mentioned in previous sections, the play is structured around either waiting for meals or recovering from them. In this case, the family is biding time waiting for dinner to be served. However, the process of having meals together breaks down over the course of the day. Breakfast goes smoothly, but then lunch is stalled for a long time as the family waits for Tyrone to return from the garden. Dinner itself is a disaster; Jamie is not even home from carousing, and Mary does not attend because she has lost her appetite as she takes more drugs. The central activity of the family eating together has fallen apart as the day has gone on.
We also see a more fully developed idea of Mary's desire for a home. We learn that she dislikes Tyrone's idea of a home so strongly because she associates it with the death of Eugene, who died when Mary was traveling with Tyrone. Mary associates Tyrone with the traveling home of the theater actor; she thus symbolically spurns the way in which she was forced to live life with Tyrone.
The more Mary uses morphine, the more she tends to delve back into past memories. We thus get a better idea of why Mary uses morphine so much it allows her to leave the present and live in the world of the past, when she was a little girl in a convent. We will see in the last act that Mary idealizes her youth so much that if she takes excessive doses of morphine, she can actually fall into a mental state in which she cannot distinguish between the past and the present. It is important to note, however, that while the men hate Mary's morphine addiction, they themselves are hardly better in their abuse of alcohol. While Mary certainly disappears mentally when she is loaded, the men do the same, even though they think their drug of choice is more acceptable. Of course, we can only assume that Mary will continue to lose more of her dreams as she gets older; O'Neill suggests in this play that people, as they get older, have a tendency to idealize the dreams of the past in such a fashion as to become disenchanted and hopelessly ineffectual in the present.
Of course, this is a very pessimistic outlook, but O'Neill clearly avoids despair by suggesting that there is some redemption through forgiveness. Mary reiterates that she cannot forget the past, but she says that she will try to forgive. While we cannot trust her to make such an effort, it seems that forgiving the past mistakes of Tyrone and her sons is the only way that Mary can stop trying to live in her past dreams and accept the present reality while thinking about a brighter future. Indeed, the title Long Day's Journey into Night has more than one meaning. If the play were simply about Mary, it could be called Long Day's Journey into the Past. There is a dual movement in the play; on one hand, the family is moving forward in time as symbolized by the passing of the day. On the other hand, all the characters, as they get increasingly drunk, travel mentally back in time to happier times when they think they had fewer problems. The title, in its ambiguous use of the word night, seems to suggest the dual nature of the play.
Act III also more clearly shows us the relationship between Edmund and Mary. It is important to recognize that Mary has never stopped seeing Edmund as her little baby son who replaced Eugene, the baby in whom Mary had so much hope. On the one hand, Mary has trouble seeing Edmund as anything other than her invulnerable baby whom she can cure of anything. The prospect of Edmund dying, however, is particularly troubling for Mary because she thinks that Edmund may be God's way of punishing her. So on the other hand, she associated Edmund with her own negligence and potential punishment from God. This double-sided viewpoint leaves complicates their relationship in a fashion that, for a literary standpoint, enriches the characterization of both Mary and Edmund.