Act III is set the next morning.
Petey sits at the kitchen table reading his newspaper. Meg calls out to him, thinking he is Stanley. When she enters and realizes it's Petey, she confesses she has run out of cornflakes and that she has a headache from the party. She also tells Petey that the drum is broken. He reassures her that she can always get another one.
Meg wants to call Stanley down to breakfast, but Petey stops her, saying, “let him sleep… this morning. Let him sleep.” Meg misses Petey’s cryptic tone, and tells him how she tried to bring Stanley his tea earlier, but was stopped in the hallway by McCann, who informed her that Stanley had already had tea. Peter interrupts her story to ask when she will go food shopping. She hurries out the door for that purpose, but quickly returns with news that a car is parked outside. Frightened, she asks if Petey had looked in the car and noticed whether there was a wheelbarrow in it. When Petey tells her it's Goldberg's car, she is relieved.
Just as Meg prepares to leave again, she hears footsteps on the stairs and thinks it is Stanley coming down for breakfast. She flutters about, distressed that she cannot offer him cornflakes. However, it turns out to be Goldberg, which upsets Meg. Goldberg assures her that Stanley will be down eventually. Meg asks him questions about his car, but Goldberg ignores her and instead speaks to Petey about the car's reliability.
After Meg leaves, Petey asks Goldberg about Stanley, and Goldberg explains that Stanley suffered a nervous breakdown at the party. Though he cannot explain why or how it happened, Goldberg is certain that is the case. Petey explains how he came home the night before to find the lights out, and had to put a “shilling in the slot” to reactive the power. He then ran into McCann, who first told him about what happened. Goldberg senses Petey's worry and reassures him that they will connect Stanley with a fellow named Monty, whom Goldberg considers the best doctor available.
Petey argues with Goldberg, suggesting Stanley should stay at the boardinghouse, but Goldberg quickly dismisses his offer. Petey exits to the kitchen as McCann enters. He has packed their bags and is anxious to leave. He refuses to “go up there again,” and says Stanley is trying to shove his broken glasses into his eyes. Petey reappears and offers to fix the glasses with Sellotape, but Goldberg again refuses his help.
Petey says he has to tend the peas in the garden, but asks to be called when Stanley comes down. However, Goldberg is adamant that Petey should be gone when they leave, and in a pleasant but anxious tone of voice, he suggests that Petey go to the pier to set up the deck chairs for tourists. Petey says he’s fine where he is, and then exits to the garden, leaving an exhausted Goldberg.
McCann picks up Petey’s newspaper and begins to shred it into strips. Goldberg demands he stop, calling the activity childish. McCann says he “wants to get it over,” and asks Goldberg whether he should bring Stanley downstairs. Goldberg ignores the question, and instead tells McCann that he feels “knocked out.” Angry at being ignored, McCann grabs the back of Goldberg’s chair and shouts at him to “get the thing done.” When Goldberg does not respond, McCann calls him "Nat," and when that does not elicit a response, calls him “Simey.” Goldberg reacts immediately and violently at this name, screaming “never call me that” as he seizes McCann by the throat.
Backpedaling, McCann denies using the name, and then asks if he should fetch Stanley. Instead of answering, Goldberg asks McCann to look in his mouth, and then claims he has never been sick and still has all of his teeth. Goldberg next reminisces about his father, whose deathbed words were, “never forget your family, for they are the rock, the constitution, the core!” Goldberg rambles a bit, and then asks McCann to blow into his mouth, which McCann does twice without question. The activity calms Goldberg down.
Lulu enters, and McCann leaves them alone, promising to return within five minutes. Lulu accuses Goldberg of using her for his perverse, sexual games. He swears he has never touched another woman, but she does not believe him. She wonders what her father would think of their sexual activity, which she does not describe. She claims that her first lover, Eddie, was respectful and never used her as Goldberg did, for a “passing fancy.” Goldberg insists their liaison was consensual, but she counters that he took advantage of her while her defenses were down. She also mentions a mysterious briefcase that Goldberg brought and which she opened out of curiosity. When McCann enters and hears her mention the briefcase, he threateningly asks her whether she has anything to confess. Goldberg senses her confusion and adds that McCann has only been “unfrocked for six months.” McCann chases her away, and the men's conversation return to Stanley’s condition.
McCann leaves the room, and quickly returns with a clean-shaven Stanley, who holds his broken glasses in his hands as he sits quietly in a chair. Goldberg compliments Stanley's appearance and promises to buy him a new pair of glasses. He and McCann then try to entice Stanley to accompany them of his own free will. They promise they want to care for him, to save him from a fate worse than death, and to make a man out of him. In an assault that mirrors the Act II interrogation, they bombard Stanley with promises which grow more ridiculous as the scene progresses. For example, they promise to gift him ear plugs, stomach pumps, and crutches while they help him skip rope.
During their speeches, Stanley remains immobile, his gaze distant. Goldberg kindly but firmly demands to know how Stanley feels about their offer to take him away. After a few moments of silence, Stanley attempts to speak but can only muster gurgling sounds. He continues to try, but ultimately drops his chin to his chest, converging in on himself as he produces nonsense words and sounds.
Goldberg gently takes Stanley in hand and leads him towards the door. Meanwhile, Petey has arrived, unnoticed, and insists they leave Stanley alone with him. Goldberg and McCann then turn towards Petey and insidiously suggest that he should accompany them as well. Though Petey does not stop them from leaving the house, he does shout, “Stan, don’t let them tell you what to do!”
Petey turns toward the table and sits down. He picks up his newspaper and begins to read. Meg enters and asks after Stanley. With trepidation in his voice, Petey lies and says Stanley is still sleeping . Meg tells him that she had a lovely time at the party, forgetting that Petey was not there. In her closing remark, Meg insists that she was the bell of the ball, and Petey agrees with her assessment.
As a whole, the structure of The Birthday Party seems very traditional. There are three acts, arranged in chronological order, and the first and third acts parallel one another. Both Act I and Act III begin with Meg and Petey's morning routine, although Act III reflects the play's descent into depravity. Meg does not have breakfast to serve in Act III, and she is frantic to remedy the oversight. As an interesting side detail, she does remember to pour Petey's tea, whereas she forgot in Act I. Because of what she has gone through since Act I, Meg is ungrounded, not so easily submerged into the superficial routine of the beginning.
In many ways, Petey is the central character of Act III, since he changes during it. At the beginning, when Meg realizes that the drum has broken but does not remember how it happened, Petey simply tells her she can get another one. There is a bit of dramatic irony since the audience realizes that the drum represents Stanley - much as it is broken, so is he mentally unstable. Petey's growth in the Act is realizing that while Meg could conceivably get a new boarder like Stanley, his particular absence will likely shatter her fragile world. The play ends with his lie to her, a lie intended to prolong her eventual breakdown. Considering the implications that Petey might have a sense of the strange Meg/Stanley relationship, his desire to maintain her illusion reveals his discovery of Stanley's importance. If she falls apart, then their pleasant, comfortable life might also fall apart.
Petey is also central because we realize he might always have had some intuition his world's sinister nature. He has largely been absent from the play thus far, and in many ways is pitiable for being a potentially willing cuckold (something Goldberg and McCann suggest to Stanley during their Act II interrogation). Yet Petey reveals an astuteness in Act III through his conversation about Stanley's mental breakdown. The fact that he is not surprised to hear Goldberg suggest it gives us reason to suspect he had seen indications of mental problems before.
When we learn that Petey is an accomplished chess player, the symbol helps us to understand him. He seems to know more than any other single character. He knows that Goldberg and McCann are not what they seem; he knows that Stanley might have mental problems; he knows that his wife's mental problems might be exacerbated if he were to end her affair with Stanley; and he realizes when he cannot win the battle to keep Stanley around. And yet he chooses to live in a pleasant stupor, to not address any of these problems. Certainly, this can be interpreted as cowardice, but it is not accidental. Like a chess player, he knows how to strategize, and has chosen a life of pleasant comfort over potential difficulties. He chooses not to live, in the sense that Goldberg accuses Stanley of in Act II, but it is a choice. When he yells to Stanley, "don't let them tell you what to do," he is in many ways describing his own life, one in which he engages nobody and hence has little responsibility. He is cowardly safe in his domestic delusion, but it is his own choice.
The Act is full of sinister images and situations. Meg's discovery of the black car brings a theatrical mystery to the fore, and she immediately interprets it as a sign of her own breakdown. She remembers Stanley's threat to have her taken away in a wheelbarrow, and worries this car is intended for that purpose. As a vehicle intended to remove debris from place to place, the wheelbarrow represents motion of unworthy objects. Meg's fear of the wheelbarrow reflects not only her fear of her own irrelevance, but also her fear of movement, of change from the comfort wherein she can maintain her delusions of importance. What is ironic is that Stanley's threat has come true not for her, but for himself. And yet her fear over the black car is not misplaced - as we can intuit from the earlier Acts, Stanley's absence might in fact compromise her own sanity.
Goldberg also reveals the depth of his sinister potential in Act III. He is able to maintain some air of charm, apparent when he assuages Meg's concerns about the car, but he refuses to answer any questions about it. His silence about certain details only deepens the aura of dread that permeates the play, both in terms of the car and in terms of other details, like the briefcase or his purpose for Stanley.
Most sinister is Goldberg's own breakdown. His world is clearly coming undone, most likely as a result of whatever sexual behavior he forced upon Lulu. Whereas he has shown nothing but suave detachment in Acts I and II, he is is a wreck in Act III, "knocked out" and undone. He is unnerved by such feelings, since he has never been sick before. He lacks his characteristic control, even lashing out at McCann for calling him "Simey." Is this sickness perhaps a sign of a guilty conscience? Or has his liaison with Lulu submerged some childhood neuroses? As he mentioned the name "Simey" as a name from his past, this latter interpretation could certainly be defended.
What Goldberg's breakdown reveals is that every person is reliant upon his own delusion, and hence subject to pain and difficulty when that delusion falters. Though he has presented himself as strong and untouchable, Goldberg centers his world around a pretense of family morals, of a nostalgia for the “old days” which were better, bigger, and more respectful. Considering the way he speaks of his mother in Act II, it is possible to interpret this delusion as an expression of childhood and control. Indeed, he shows a desire to be something of a parent both to Stanley, whom he forces into an infantile state of confusion and fear, and to Lulu, who he treated as a daughter in Act II and then as a prostitute in Act III. Lulu's confrontation leads Goldberg into further lies about her compliance, a situation he does not handle well until McCann finally chases her away. Interestingly, his final tactic is to elicit a confession from her. In a world where we are guilty of our own delusions and sins, forced confession becomes a threat.
Stanley's situation also reveals the sinister nature of the play. Ironically, he is most frightening because he is suddenly so presentable. The reprise of their Act II interrogation now has the sense less of attack and more of a bedside vigil. All of his delusions shattered, Stanley can only receive these promises silently. With repeated readings or viewings of the play, an audience might realize how Stanley's breakdown could be any person's fate if he or she were forced to confront his or her past sins and delusions too forcibly. From this perspective, the scene is even more horrifying.
At the end, Meg remains blissfully unaware of the situation. It is telling that the play ends with a confirmation of her delusion. The final exchange is full of dramatic irony - she has constructed a reality that we know to be false, both because Meg was not the belle of the ball, and because Petey was not there to know it. The play ends with a scenario of ambiguity and delusion, which falls perfectly in line with the themes it explores throughout.
In a published speech entitled “Writing for the Theatre,” Pinter offered that Petey’s exclamation - “Stan, don’t let them tell you what to do!” - defined his mindset, his plays, and his entire career. Neither Pinter nor his characters conform to established means of interpretation, and he makes every effort to avoid easy answers that could be interpreted as the author's moral message. Instead, we are to leave Pinter's plays - The Birthday Party included - unsure exactly what is true, both about the character on stage and about ourselves.