The scene is the same as at the end of Act 2. Eric is standing near the entrance of the room and asks if they know. The Inspector confirms that they do, and Sheila reveals that their mother placed blame on whichever young man got the girl into trouble. Eric bitterly accuses his mother of making it difficult for him, and Mrs. Birling defends that she couldn’t have known the man in question was him, as he’s not the kind of person to get drunk. Sheila corrects her as she did before, which prompts Eric to blame Sheila for betraying his drinking habits. The Birling parents begin accusing Sheila of family disloyalty, when the Inspector cuts them off and encourages them to address their family relationships after he’s finished.
Intra-family antagonisms ensue when Eric learns that both his mother and sister have betrayed him. The Inspector has to ask the Birling family to sort through their private problems after he has cleared up the more public problems that he is addressing in the investigation.
Eric pours himself a drink and begins to explain his story: he met the girl the previous November in the Palace bar, while he was “a bit squiffy,” and started talking to her. He clarifies that she wasn’t there to “solicit.” He went back to her place that night. At her father’s insistence, Sheila removes her mother from the room. Eric continues: he saw the girl a number of times after, and one of the times, she told him she was pregnant. The girl didn’t want to marry him because he didn’t love her. He gave her fifty pounds to support her.
Eric’s relationship with Eva Smith was very similar to Gerald’s, but was different enough to render his actions punishable: like Gerald, he met her at a bar and then continued to see and sleep with her; unlike Gerald, however, he incidentally got her pregnant. Also like Gerald, he tried to be responsible in providing the girl with money; unlike Gerald, however, (as will soon be seen), the money he provided was obtained illegally.
When Mr. Birling asks where the fifty pounds came from, Eric confesses that he took it from his father’s office. Mrs. Birling enters again, curious, and her husband informs her of both of the son’s wrongdoings—impregnating the girl and stealing Birling’s money. Eric explains that he got the money by collecting small accounts, giving the firm’s receipt, and then keeping the money for himself. When his father asks him why he didn’t just ask him for help, Eric replies that he’s not the “kind of father a chap could go to when he’s in trouble.”
Eric is the first of the Birlings to be accused of committing a legal crime. The other Birlings did things that were immoral, but none that necessarily defied a law. Because of the definable illegality of Eric’s wrongdoing, the Birling parents will be more upset with him than they were with Sheila or with each other.
The Inspector leadingly asks Eric if the girl found out that his money had been stolen, and Eric says that she had and that she refused to see him afterward, but then he asks how the Inspector had known that. Sheila reveals that Mrs. Birling sat on the committee that assessed the girl’s need for aid. Eric turns to his mother to blame her for the girl’s suicide and begins to threaten her.
Eric avenges the blame that his mother placed on him by returning the gesture and blaming her in turn. At the same time, the girl who Mrs. Birling refused aid turned down on account of her low morals now is revealed as quite moral—refusing money in a time of need. The girl's use of the name Mrs. Birling in front of the charity organization also takes on a new light, as she may have been referencing the fact that she was carrying Eric Birling's child.
The Inspector states that he does not need to know any more, and reminds the family that each member is responsible for the death of Eva Smith. He tells them to never forget it. Mr. Birling offers the Inspector a bribe of thousands of pounds, but the Inspector refuses it.
The Inspector’s departing reminder makes it seem as though the main project of his inspection all along was to convince the Birling family of the immorality of their separate actions toward Eva Smith, of their responsibilities as people with wealth and power and as people in general. Birling, with his bribe, continues to try to use power and influence to evade responsibility.
The Inspector deduces a moral from the investigation—though Eva Smith has gone, there are millions and millions of Eva Smiths still alive, who have hopes and suffering and aspirations, and who are all implicated in what we think, say, and do. He insists that everyone is responsible for each other, and then walks out.
The Inspector speaks in the vein of the people that Mr. Birling positioned himself against in the beginning of the play, strongly asserting the fundamental humanity of all people and therefore the responsibility of everyone for everyone.
Sheila is left crying, Mrs. Birling is collapsed in a chair, Eric is brooding, and Birling pours himself a drink and then tells Eric that he considers him to be most blameful. He fears for the public scandal that will surely result from the investigation and that might harm his chances at a knighthood. Eric asks what difference it makes if he gets a knighthood now; Birling warns Eric that he’ll be required to repay everything he’s stolen and work for nothing until he has.
The Birlings recover from this bombardment of information. Mr. Birling places most blame on Eric, presumably because his contribution to the affair –given its illegality—will result in the greatest social scandal and will do most harm to the family’s name.
Sheila is upset that her parents are acting as though nothing has happened. She then wonders aloud whether the Inspector wasn’t actually a police inspector at all. Birling judges that it would make a big difference if the Inspector had been a fake, while Sheila judges that it wouldn’t, because what is really important are the truths revealed by the questioning. Birling recalls that the Inspector did talk like a Socialist.
Sheila and Mr. Birling split in their respective opinions of the moral consequence of the Birlings’ actions; Sheila thinks that they have ethical significance regardless of their legal assessment; Birling, on the other hand, cares only about the legal and social consequences.
Edna announces Gerald’s entrance. Gerald inquires how the Inspector behaved with them since his departure, and then he reveals that the Inspector wasn’t a real police officer. Gerald met a police sergeant on his walk and asked him about Inspector Goole; the Sergeant swore that there was no inspector by the same name or description.
Gerald confirms Sheila’s earlier hypothesis that the Inspector was bluffing about his affiliation with the police department. Suddenly the legal ramifications of what the Inspector revealed disappear.
The Birling parents are very excited by this news, and Birling calls Chief Constable to verify that there is no Inspector whose name is Goole or who matches his description. Birling exclaims that this makes all the difference, and again Sheila and Eric insist that it doesn’t. Birling reasons that the inspection was probably set up by someone in the town who doesn’t like him.
The removal of the legal (and therefore social) consequences of what has happened widens the split between the family members. The Birling parents care about their position, and therefore when the legal issues are gone consider themselves home free. Eric and Sheila, who care about Eva Smith herself and the basic morality of the Birlings' actions, don't agree.
Mrs. Birling reminds her family that she was the only one who didn’t give in to him, and suggests that they now discuss the affair amongst them and determine if there is anything to do about it. Birling agrees with his wife, and adds that that the Inspector may not be the end of it.
Mrs. Birling sees the interaction with the Inspector as one based on power: only she didn't give in to him. Now she wants to keep the entire affair private and handle it themselves (and also prepare to deal with any other consequences beyond the Inspector).
Birling demands that Eric, who is looking sulky, begin to take some interest in the matter. Eric responds that his problem is rather that he’s taken too much interest, and Sheila joins him in this sentiment. Mr. Birling and Mrs. Birling voice their desire to “behave sensibly” in the circumstance, but their children rebut that they can’t pretend that nothing’s happened, when the girl is still dead and the family members still did the things they confessed to doing. Both sides continue to protest and defend their own positions.
The rift widens between the older Birlings who wish to put their deeds and the inspection behind them, and those (the children) who cannot forget what they've done and what happened to the girl with whom they were connected.
Gerald proposes that the one fact that Eric and Sheila are assigning great significance—that Eva Smith is dead—may not even be a fact after all. He asks the Birlings how they know that they’ve all committed offenses to the same girl, suggesting that the photographs the Inspector showed the family members might actually have been distinct photographs, and not of the same girl. Birling catches on, and reasons that they only had the Inspector’s word for it, but now that they know that he lied about his identity, he might well have been lying about it all.
Gerald's hypotheses turns the philosophical and moral screw of the play even further: if Eva was not a single individual and there was no suicide, then there were no dire consequences. The play has already created a contrast between legality and morality. Now it asks the question of whether immoral behavior is less immoral if there are no serious consequences. Gerald and Birling seem to think not.
Gerald asks what happened after he’d left. Mrs. Birling recounts that the Inspector accused her of seeing Eva Smith only two weeks previous, and that she had assented even though the girl hadn’t called herself Eva Smith before the Committee. She admits that she had felt compelled to provide what the Inspector expected from her.
Mrs. Birling revisits her performance in the questioning, and retrospectively sees that she had been manipulated into answering as the Inspector wanted her to; she thus tries to use the Inspector’s newfound guilt to bolster her own innocence.
Eric still doesn’t believe Gerald’s claim, and insists that the girl that he got pregnant was the same that asked his mother for aid. Gerald proposes that even that could have been nonsense. Eric fights back, arguing that it’s not nonsense because the girl’s still dead, but Gerald asks “what girl?” Eric still holds to the idea that the girl he knew is dead, even though he has no evidence for it apart from the Inspector’s testimony.
Even though Eric should logically be the most relieved, he is also the least willing to dismiss the girl’s suicide as an invented hoax, likely because he feels guiltiest for the offenses that he committed. It's almost like Eric needs the consequence in order to feel the guilt he knows he should feel.
Birling triumphantly continues to hypothesize that the Inspector simply shocked them into submission with his initial description of the girl’s suicide, in order to more easily bluff them throughout his inquiry. Gerald suggests that they call the Infirmary to confirm whether or not there was any suicide at all, and though Birling objects that it will look “queer,” he proceeds, and discovers from the hospital that they haven’t had a suicide for months.
Again, the case is further unraveled, and its ethical significance further confused, when it turns out that no suicide took place. Yet, oddly, as Eva Smith ceases to be a real person, she becomes even more of a symbol of all poor women and people affected by the blind and uncaring power of the rich.
Gerald, Mr. Birling, and Mrs. Birling relax at this news and pour themselves a drink. Sheila refuses to celebrate, and continues to claim that what has happened remains important, and that it was only lucky that it didn’t end tragically this time. Eric joins her in refusing to pretend that everything is as it was before. Sheila articulates that she can’t forget what the Inspector said and how he made her feel, and that it frightens her that her parents can so easily forget it. She refuses Gerald’s offer to renew their engagement.
In contrast to their parents and Gerald, Sheila and Eric firmly believe that the investigation and the truths it revealed remain significant. They take the position that t that uncaring acts toward others that could result in harm to others, even if no such harm occurs, are immoral and must be responded to as such. Sheila's refusal to renew her engagement to Gerald is a refusal to go back to the unthinking, comfortable state she occupied before.
Just as Birling begins to make fun of his overly serious children, the telephone rings. After Birling hangs up, he reports that it was the police, alerting him that a girl has just died on her way to the infirmary, after swallowing some disinfectant, and that a Police Inspector is on his way to ask some questions. The Birlings stare “guiltily and dumbfounded.” As Sheila rises to stand, the curtain falls slowly.
The play concludes on an ambiguous note: did the Inspector know that a girl had or was going to commit suicide by disinfectant, or is the play just a constructed political allegory that ultimately proves Sheila’s point:“If it didn’t end tragically, then that’s lucky for us. But it might have done”? Taken symbolically, it's possible to see this sudden death as a response to the question about morality when there are no consequences: that even if some immoral acts based on denying the humanity of others don't produce consequences, they will eventually result in consequences, not just for those harmed but for those like the Birlings who do the harming. Sheila standing as the curtain falls seems to indicate not just her willingness but her desire that the Birlings be forced to face what they have done.