The play begins in the living room of a seaside boardinghouse in 1950s England. Petey, the boardinghouse owner, and his wife Meg, both in their sixties, sit at the living room table and engage in tepid conversation while eating breakfast. Meg is an inquisitive character who peppers Petey with repeated questions concerning his food, his job, etc. Petey informs his wife that two gentlemen will soon arrive to stay at the boardinghouse; he met them the night before. Meg is flustered by the news at first, but quickly recovers to promise she will have a room ready for them.
She then calls out to Stanley Webber, their boarder who is asleep upstairs. When he doesn’t answer, she goes upstairs to fetch him, and then returns a bit disheveled but amused. Stanley, a bespectacled, unkempt, surly man in his thirties, soon follows. Petey and Stanley speak of mundane topics while Meg prepares cornflakes and fried bread for Stanley’s breakfast. After Petey leaves for work, the atmosphere changes. Meg flirts with Stanley, who jokingly calls her “succulent” while criticizing her housework. When Meg becomes affectionate, he rudely pushes her away and insults her. Meg then informs him that two gentlemen are coming. The news unsettles Stanley, who has been the only boarder for years. He accuses Meg of lying, but she insists that she speaks the truth.
Before Meg leaves to shop, Lulu, a young girl in her twenties, arrives with a package. Meg instructs Lulu to keep the package from Stanley, and then she leaves. Lulu and Stanley chat for a little while, mostly about Stanley’s lack of enthusiasm and his appearance. Lulu calls him a “wash out” and then quickly exits. Stanley washes his face in the kitchen, and then leaves by the kitchen door. In the meantime, Goldberg and McCann enter the living room. They are the two gentlemen who had requested rooms for the evening.
It becomes immediately apparent that Goldberg and McCann have come under mysterious circumstances to “finish a job.” The job in question seems to be Stanley, though details are scarce. Goldberg reassures McCann that they are at the right house, and that this job will cause no more stress than their jobs usually cause them. Goldberg rambles on about his uncle until Meg arrives, and introductions are made.
Goldberg’s sweet temperament and suave demeanor soon set Meg at ease. Goldberg asks after Stanley, and Meg tells him that Stanley was once a successful pianist but had to give it up. Meg also reveals that it is Stanley’s birthday, and Goldberg suggests they have a party. Thrilled with the idea, Meg shows the gentlemen to their room. Later, Stanley returns to the living room as Meg arrives to put the groceries away. She tells him about the two gentlemen, and Stanley is visibly upset to learn Goldberg’s name. To cheer him up, Meg suggests he open his birthday present, even though Stanley insists that it is not his birthday. To humor Meg, he opens the package and finds a toy drum with drumsticks. He hangs the drum around his neck and parades around the table beating the drum merrily until his rhythm becomes erratic and chaotic. He beats the drum possessively and looms over Meg with a crazed expression on his face.
Later that same evening, McCann sits at the living room table shredding a newspaper into five equal strips. Stanley arrives, and the two men awkwardly greet one another. McCann, in a calm tone of voice, congratulates Stanley on his birthday, and says it is an honor to be invited to his party. Stanley replies that he wants to spend the evening alone and tries to leave, but McCann will not let him.
Stanley sits at the table and touches one of the newspaper strips, which upsets McCann. Stanley speaks of his past, and suggests he has never been one to cause trouble. Stanley insists that he has met McCann before, and grows upset when McCann denies the connection. Stanley wants to know why he and Goldberg are at the boardinghouse, and grows frantic when McCann claims they are there on a short holiday. Desperate, Stanley grabs McCann’s arm, who violently hits him off. Shocked into submission, Stanley calms himself and speaks of his love for Ireland, for its people, its sunsets, and its police. He asks McCann to accompany him to a nearby pub, but is interrupted when Petey and Goldberg enter the room.
Petey introduces Stanley to Goldberg, and then leaves. The situation in the room grows tense, as Goldberg yammers on about his past. Despite Goldberg’s soothing words, Stanley remains on edge and refuses to sit down when McCann asks him to. It is not McCann's threats that convince him to sit, but rather Goldberg's quiet insistence.
After Stanley submits, Goldberg and McCann interrogate him about his past - they accuse him of betraying their “organization,” of killing his wife, of leaving his bride at the altar, of being a waste of space, and more. Stanley answers at first, but is soon struck dumb by the sheer number of questions being thrown at him. The questions grow progressively more ridiculous and nonsensical. Finally, Stanley hits Goldberg in the stomach. McCann and Stanley threaten each other with chairs, but are cooed back into civility when Meg arrives, beating Stanley’s toy drum. She is dressed for his birthday party. Goldberg compliments her, and the tense atmosphere quickly dissipates as Meg makes a moving tribute to Stanley in a toast while McCann flashes a torch in Stanley’s face like a spotlight. Lulu arrives, and Goldberg gives a second toast which includes more reminiscing.
The party begins in earnest. Lulu and Goldberg flirt, while Meg and McCann speak of Ireland. Stanley sits alone at the table until Meg suggests they all play blind man’s buff. During Stanley’s turn, he is blindfolded by McCann, who breaks his glasses and puts the toy drum in his path so that Stanley’s foot smashes through it. When Stanley reaches Meg, he begins to strangle her. Goldberg and McCann pull him off, but then the lights suddenly go out. In the darkness, the two gentlemen cannot find Lulu, who has screamed and fainted. McCann shines his flashlight on the table to discover Stanley standing over Lulu as though about to sexually assault her. He giggles manically as the men slowly approach him and the curtain closes.
The next morning, Petey sits at the living room table reading a newspaper, while Meg frets about having no breakfast food left. Her memory is hazy from the night before, and she forgets that Petey was not there as she tries to remember what happened. When she leaves to shop, she sees Goldberg's car in the driveway, and grows frightened. Petey calms her down.
As Meg prepares to leave again, Goldberg enters the room and sits at the table. Meg asks him about the car, but he ignores her. She finally leaves. Petey asks Goldberg about Stanley, and Goldberg explains that Stanley suffered a nervous breakdown, and needs to be taken to a doctor whom Goldberg knows. Petey wants to see Stanley when he wakes, despite Goldberg's insistence that he should simply leave for work.
McCann enters with two suitcases, and tells Goldberg that Stanley is trying to fit his broken glasses into his eyes. When Petey suggests a way to fix the glasses and offers to fetch a doctor, Goldberg dismisses him. Petey departs to tend to his peas, insisting he be told when Stanley wakes, and Goldberg sits slumped over the table.
McCann demands they expedite the job, but Goldberg ignores him. Angry, McCann shakes Goldberg's chair and calls him "Simey," which causes the latter to attack him. McCann pacifies Goldberg, who then admits he feels poorly and is confused by the feeling. He tells McCann about his father and about his own principles on family, and finally makes a strange request by asking McCann to blow into his mouth twice. McCann does so without question, and Goldberg is calmed.
Lulu enters, and McCann leaves them alone. Lulu accuses Goldberg of having taken sexual advantage of her the night before. They argue over blame until McCann reenters and tells Lulu to confess her sins. Startled by this bizarre turn of events, Lulu flees. McCann then leaves to fetch Stanley, who enters cleanly shaven and nicely dressed. The two men seem to take pity on Stanley, and Goldberg promises to buy him new glasses. In a reprise of the interrogation from Act II, they pepper Stanley with gentler questions and comments. Goldberg asks Stanley if he wants to leave with them, but Stanley can only muster gurgling sounds. They begin to exit with Stanley, but Petey arrives and tells them to stop. Menacingly, they ask Petey if he wants to accompany them. Petey allows the two men to take Stanley away, but before they leave, he cries out “Stan, don’t let them tell you what to do!”
Afterward, Petey returns to the living room table and picks up his newspaper. Meg arrives and asks if Stanley has come down to breakfast yet. Petey lies and tells her Stanley is still sleeping.