Peter goes into Melbourne for a meeting with Dwight. Mary insists that Peter take throat lozenges so he does not get sick from the radiation that has reached the city. He does not have the heart to tell her that the radiation is already all around them in their home.
At the meeting, Dwight takes the Scorpion out of Australian control, and he announces his plan to take the boat into international waters to sink it. Peter asks Dwight if he will need a tugboat to take the crew back, but Dwight says that it is not necessary. When the two men say goodbye, Dwight tells Peter that he is going home to America.
John visits his elderly mother, who is already sick and dying from the radiation. She is worried that her dog will keep on living after she is gone, with nobody to take care of it. John leaves her to go to his office and read the daily radiation report. He tries to find milk for his mother, but every store is out. When John returns to his mother's home, he finds that she has written a loving note to him and taken a cyanide pill while he is gone. He is surprised to find that she had obtained the pills without his knowledge. Then, John goes to the nearest pharmacy and takes some pills and a syringe from the counter. He returns to his mother's house and uses the syringe to put her dog to sleep.
At the Holmes house, baby Jennifer cries all night and then vomits in the morning. Both Peter and Mary begin to get sick also, but they try to hide their sickness from each other. Peter is surprised to find Mary singing, and she admits she feels lucky that they all have gotten the sickness at the same time, rather than any of them outliving each other.
The next day, Peter goes to Melbourne to meet John at the Pastoral Club. Peter tells John he is feeling better, but John says that the recovery will only last for a few days before a relapse. John leaves the club, picks up some cyanide pills, and then goes to the garage where he keeps his Ferrari. He tunes up the Ferrari, puts on his crash helmet and goggles, gets in the driver's seat, and takes the pills.
Meanwhile, Peter picks up a garden seat from a hardware store in Melbourne and then drives home. He is still feeling much better, but he does not tell Mary, who is very sick. He shows her the garden seat and then makes the house cozy with a fire. Mary and Peter talk about the war. Peter says that Australia gave Britain moral support, so, in a way, their country was at least indirectly involved in the war.
Mary wants to know if there was any way to stop things from spiraling out of control. Peter says there is no way to stop millions of people who think they need to defend their national honor by dropping bombs. He thinks that education is the only thing that might have prevented things: newspapers could have helped educate people, but chose instead to fill their pages with stupid, superficial stories. Governments were not wise enough to encourage the newspapers to educate people about real issues.
Even though Peter is feeling better, he cannot imagine what he would do if he lived on even a few days after Mary and Jennifer die. After talking with Mary, Peter injects Jennifer with the syringe. He takes the baby into bed with him and Mary. The parents say a last goodbye to each other, saying they love each other and that they have had a wonderful time in their marriage. Peter and Mary then take their pills, lying next to each other in bed.
That night, Dwight and Moira talk. Both are very sick. The next day, Moira says goodbye to her sick parents and drives out to meet Dwight. Moira asks Dwight if she can accompany him on the submarine's last voyage. Dwight refuses, saying that he cannot let her come because it is against U.S. Navy's regulations. He says he has never broken the rules, and he does not want to do so now.
Dwight and Moira kiss and say their last goodbye. Moira says she will see Dwight in Connecticut someday. She drives out to a cliff overlooking the ocean so she can see the submarine leave the harbor and sink. As soon as the ship goes under, Moira, sitting in her car, takes out a bottle of brandy and swallows her pill.
Though the ending of On the Beach is no surprise, we may find ourselves feeling as the characters do, unable to believe the reality of the war's aftermath and the fact that all of humankind will cease to exist. Shute, however, has been relentless from the start in leading us to the moments when all the main characters die. Just as the novel's epigraph promises, the world ends "not with a bang, but a whimper." Just as there is no escape for the characters, there is no relief for us as we hope for some plot-twisting miracle. The only surprise may be that all the characters commit suicide or are euthanized. Suicide is the ultimate act of individual self-destruction, just as nuclear war is the ultimate act of humanity's self-destruction. Interestingly, Shute does not have the characters debate the ethics of taking the pills—they all just accept the pills, and use them. Perhaps the characters do so because they see suicide as the only means they have to exert control over their powerless situation. With the pills, they can decide where, how, and with whom they spend their last moments.
Mary, Peter, and Jennifer die together in bed, so that the family may stay together until the end. More than anything, Peter and Mary fear dying at separate times, unable to bear the prospect of enduring any days alone after the other has gone. Both John and Moira choose to die in cars: even in their last moments, neither can part with the creations of a technological society. Moira dies with a brandy and a pill in her car, ironically showcasing the "best" of human creations. Both John and Moira die alone—lonely at their deaths as they have been in life. Even at the last moment, Dwight refuses to break the Navy's rules; his need for obedience and order in his life is greater than his need for comfort from Moira in his dying moments. Indeed, even in their last moments, seemingly all the characters restrain their emotions. Moira pulls away from Dwight to avoid prolonging the agony of a goodbye, not giving herself or Dwight time to fully feel the sorrow of their parting. John only allows himself a few tears when he finds his mother dead. It is surprising to see the characters handle this unbelievable tragedy in such a calm and logical manner.
Throughout On the Beach, the war, though accidental, is presented as inevitable. From the characters' conversations, we get no sense that anything could have been done to prevent it. In this chapter, however, Shute finally provides a way out, a means by which the nuclear war might have been prevented. Peter mentions that newspapers could have prevented the war, if the papers' articles actually educated people about how to achieve peace in the world, rather than dwelling on superficial, sensationalist headlines that distracted people from the real issues. Peter blames governments for not using newspapers properly, though, oddly, he does not condemn ordinary citizens for not demanding more from their newspapers. Indeed, most citizens are like Mary, who in Chapter Eight ignores the news on the radio because she does not want to hear anything pessimistic. With On the Beach, Shute means to educate us about the dangers of ignoring world events, and to set forth a scenario that the mainstream media might never consider. Shute sees fiction as an effective means of educating us about the dangers of nuclear weapons, and he wants us to understand that the inevitable will come about if we do not learn how to stop it now.