Chris tries to insist that he will marry Ann, but Kate finally tells him that if Larry is dead, Joe killed him. Chris understands this to mean that Joe was guilty of shipping the faulty parts. Which means that Joe would have been responsible for Larry's death. Keller at last admits his guilt, but justifies his actions saying that if he had done it for his family. And if he went that day the factory would have been shut down and he would have lost money needed to support his family. Chris rejects this explanation, telling Joe that his responsibility to his country sometimes outweighs that to his business and family. Chris storms off, leaving Joe worn out and heart brokenly guilty.

Kate waits on the back porch for Chris- he took the car six hours before and has not come back yet. Jim enters and consoles Kate before the entrance of Joe. Ann has stayed in her room for those six hours: having seen Chris storm out of the house, she now knows the truth about Keller’s guilt. Joe insists that Chris just doesn't understand what responsibility for family means, and that Larry knew better what the business was all about. Joe tells Kate that he did it all for her and their two sons.

When Ann emerges, she asks Kate to tell Chris that she knows Larry is dead, so that Chris will no longer feel ashamed about his love for Ann. Kate still insists that Larry is alive; Ann insists that she loved him and wouldn't have even considered marrying anyone else if she weren't sure he'd died. Finally, Ann asks Joe to go into the house and produces a letter that Larry wrote her the day he died; she tells Kate that she didn't bring the letter to hurt the family, but both are devastated by the final destruction of Kate's hope.

Chris returns and tells Ann and Kate that he is going away to Cleveland to start over; he rejects Ann when she begs to go with him, saying that he can no longer bear to look at his father but can also not bring himself to send him to prison as he deserves and therefore is not a moral and strong enough man for her. When Joe enters, he confronts Chris and they argue about Joe's guilt. Ann rushes forward and gives Larry's letter to Chris; Kate tries to take it away from him and to prevent Joe from hearing it, but it is too late. Chris reads the letter aloud: it describes how, upon learning about the investigation into the incident and his realization of his father's guilt, Larry couldn't bear to live anymore; he told Ann that he knew he'd be reported missing and that she mustn't wait for him. All realize that Joe was responsible for Larry's death: Although Larry's plane did not have a cracked cylinder head in it, Larry found out that his father was not the kind of man he thought he'd been. He took his own life by crashing his plane during a mission rather than face the disillusionment he could now see through. On hearing this news, Keller goes inside the house to get his jacket and turn himself in; but while Chris and Kate argue about sending him to prison and Ann watches the results of the letter unfold, a shot is heard. Joe has committed suicide. Ann runs off to find Dr. Bayliss, and Chris and Kate are left alone in a final tableau of their grief.

The precise date of events in the play are unclear, however it is possible to construct a timeline of the back-story to All My Sons using the dialogue of the play. The play is set in August 1946, in the mid-west of the USA with the main story set between Sunday morning and a little after two o'clock the following morning.

Arthur Miller’s writing in All My Sons often shows great respect for the great Grecian tragedies of the likes of Aeschylus, Sophocles and Euripides. In these plays the tragic hero or protagonist will commit an offence, often unknowingly, which will return to haunt him, sometimes many years later. The play encapsulates all the fallout from the offense into a 24 hour time span. During that day, the protagonist must learn his fault and suffer as a result, and perhaps even die. In this way the gods are shown to be just and moral order is restored. In All My Sons, these elements are all present; it takes place within a 24 hour period, has a protagonist suffering from a previous offense, and punishment for that offense. Additionally, it explores the father-son relationship, also a common theme in Grecian tragedies. Ann Deever could also be seen to parallel a messenger as her letter is proof of Larry's death.

The Greek plays, and those of Shakespeare two thousand years later, are about kings, dukes or great generals, because at that time these individuals were thought to embody or represent the whole people. Nowadays, we do not perceive the upper classes as most representational. When writers want to show a person who represents a nation or class, they typically invent a fictional “ordinary” person, the Man in the Street or Joe Public.

In Joe Keller, Arthur Miller creates just such a representative type. Joe is a very ordinary man, decent, hard-working and charitable, a man no-one could dislike. But, like the protagonist of the ancient drama, he has a flaw or weakness. This, in turn, causes him to act wrongly. He is forced to accept responsibility - his suicide is necessary to restore the moral order of the universe, and allows his son, Chris, to live free from guilt and persecution. Arthur Miller later uses the everyman in a criticism of the American Dream in Death of a Salesman, which is in many ways similar to All My Sons.

The play focuses on Joe Keller’s conflict of responsibilities, his responsibility to his family and that to wider society. He originally believes that he is justified in sending cracked cylinder heads and causing the deaths of 21 pilots, as this allowed his family to make money and allowed his son Chris to inherit the family business.