The play begins in August, 1912, at the summer home of the Tyrone family. The setting for all four acts is the family's living room, which is adjacent to the kitchen and dining room. There is also a staircase just off stage, which leads to the upper-level bedrooms. It is 8:30 am, and the family has just finished breakfast in the dining room. While Jamie and Edmund linger offstage, Tyrone and Mary enter and embrace, and Mary comments on being pleased with her recent weight gain even though she is eating less food. Tyrone and Mary make conversation, which leads to a brief argument about Tyrone's tendency to spend money on real estate investing. They are interrupted by the sound of Edmund, who is having a coughing fit in the next room. Although Mary remarks that he merely has a bad cold, Tyrone's body language indicates that he may know more about Edmund's sickness than Mary. Nevertheless, Tyrone tells Mary that she must take care of herself and focus on getting better rather than getting upset about Edmund. Mary immediately becomes defensive, saying, "There's nothing to be upset about. What makes you think I'm upset?" Tyrone drops the subject and tells Mary that he is glad to have her "dear old self" back again.
Edmund and Jamie are heard laughing in the next room, and Tyrone immediately grows bitter, assuming they are making jokes about him. Edmund and Jamie enter, and we see that, even though he is just 23 years old, Edmund is "plainly in bad health" and nervous. Upon entering, Jamie begins to stare at his mother, thinking that she is looking much better. The conversation turns spiteful, however, when the sons begin to make fun of Tyrone's loud snoring, a subject about which he is sensitive, driving him to anger. Edmund tells him to calm down, leading to an argument between the two. Tyrone then turns on Jamie, attacking him for his lack of ambition and laziness. To calm things down, Edmund tells a funny story about a tenant named Shaughnessy on the Tyrone family land in Ireland, where the family's origins lie. Tyrone is not amused by the anecdote, however, because he could be the subject of a lawsuit related to ownership of the land. He attacks Edmund again, calling his comments socialist. Edmund gets upsets and exits in a fit of coughing. Jamie points out that Edmund is really sick, a comment which Tyrone responds to with a "shut up" look, as though trying to prevent Mary from finding out something. Mary tells them that, despite what any doctor may say, she believes that Edmund has nothing more than a bad cold. Mary has a deep distrust for doctors. Tyrone and Jamie begin to stare at her again, making her self-conscious. Mary reflects on her faded beauty, recognizing that she is in the stages of decline.
As Mary exits, Tyrone chastises Jamie for suggesting that Edmund really may be ill in front of Mary, who is not supposed to worry during her recovery from her addiction to morphine. Jamie and Tyrone both suspect that Edmund has consumption (better known today as tuberculosis), and Jamie thinks it unwise to allow Mary to keep fooling herself. Jamie and Tyrone argue over Edmund's doctor, Doc Hardy, who charges very little for his services. Jamie accuses Tyrone of getting the cheapest doctor, without regard to quality, simply because he is a penny-pincher. Tyrone retorts that Jamie always thinks the worst of everyone, and that Jamie does not understand the value of a dollar because he has always been able to take comfortable living for granted. Tyrone, by contrast, had to work his own way up from the streets. Jamie only squanders loads of money on whores and liquor in town. Jamie argues back that Tyrone squanders money on real estate speculation, although Tyrone points out that most of his holdings are mortgaged. Tyrone accuses Jamie of laziness and criticizes his failure to succeed at anything. Jamie was expelled from several colleges in his younger years, and he never shows any gratitude towards his father; Tyrone thinks that he is a bad influence on Edmund. Jamie counters that he has always tried to teach Edmund to lead a life different from that which Jamie leads.
O'Neill's opening stage directions immediately give the audience some clues as to what the Tyrone family is like. The bookshelves, for instance, show that the family is both educated and worldly; there are books by a wide range of famous European authors. The Irish literature on the bookshelf clues us in to the family's pride in its Irish heritage. The character descriptions also foreshadow some of the play's conflicts. Mary is described as decaying, yet she stills retains a "youthfulness she has never lost." We see that she is in a transition period in her life, on the verge of becoming an old woman. The description of Tyrone and his shabby, utilitarian clothes suggests his financial prudence. He has obviously taken care of himself, because he looks ten years younger than his age. In fact, Tyrone does not seem to be affected physically by the passage of time; he maintains the digestion of a 25-year-old, for instance. His impervious body may support the idea that Tyrone has not changed very much throughout his life despite Mary's continual efforts to make him reform some of his attitudes and habits. Notice that O'Neill uses stage directions more than many other playwrights to provide insight into what the characters ought to look like and what their central interests are.
It is also important when beginning the play to notice that O'Neill does not condemn any one of these characters more than any other. Instead, he feels a great sympathy for all four Tyrones, as he wrote to his wife in 1940 when he completed the play. All the characters have severe faults, and all are capable of great cruelty. At the same time, they are all part of one family that has stayed together throughout many years of hardship, and they can all be very loving and compassionate. One cannot single out any particular character as the protagonist or antagonist; one can instead see the themes that create strife in the family and the ways the family mends itself when it falls into disorder.
There are two major health problems in the play, which will slowly be uncovered over the course of the four acts, but they are both hinted early on. The first is Edmund's consumption. We see that he is having coughing fits in the morning, and, even though Mary insists that he has merely a bad cold, we will learn later on that he is undoubtedly inflicted with tuberculosis and will have to live in a sanatorium in order to be cured. The second problem in the play is Mary's addiction to morphine, which began when a doctor prescribed the drug to her after she gave birth to Edmund as a means of stopping her intense pain. As this play opens, Mary has just returned from a long treatment program designed to break her addiction. She shows signs of recovering--she is gaining weight again--but we will learn later on in the play that she has quickly become a full-blown morphine addict once again.