When Dwight returns to Melbourne, he gets a draft operation order for the submarine's mission. They will take a two-month cruise to the west coast of the United States, stopping in Panama, San Diego, San Francisco, Seattle, and Alaska, returning to Melbourne via Pearl Harbor. They will be gone from April to June. The mission of the cruise is to attempt to determine the validity of the Jorgensen effect, a controversial theory espoused by some scientists that the rain and snow in the Northern Hemisphere have washed the radiation out of the air and slowed the approach of radiation to Australia.

After the mission briefing, John shows Peter a Ferrari racecar he has just purchased. He has always dreamed about racing cars, but he could never justify the hobby financially. Now that he has so little time left, he has decided he wants to fulfill his dream, regardless of the cost.

Peter then goes to the local pharmacist to ask him about the symptoms and onset of radiation sickness. Peter wants to know how he can help Mary prepare for suicide in the event that the radiation reaches Melbourne while he is still away at sea. The pharmacist says that radiation sickness is characterized by nausea, vomiting, and diarrhea, which grows progressively worse over the course of bout a week until the victim dies of dehydration and exhaustion. Because death from radiation is unpleasant and prolonged, the pharmacist has a supply of cyanide pills and syringes to give out to the population should they want to end their lives with more dignity. The pharmacist gives Peter two dummy pills for Mary and a syringe for Jennifer. When the time comes, Mary can come back and get the real cyanide.


Earlier, in Chapter Three, the characters debate the reasons for recording the history of the war. Here in Chapter Four, they discuss what human knowledge should be recorded in the event that life ever returns to the planet. Moira highlights the dangers of knowledge when she flippantly asks if historians will record an explanation of how to make a cobalt bomb. While science is often beneficial to human society, technology has also led to its ruin. At this point, the radiation is the only meaningful, lasting legacy of scientific knowledge. Shute compares the danger of human creation to the magnificence of nature. Right after Moira's comment, Dwight remarks that they should not waste the beautiful, warm water in the ocean. The beauty of the beach makes it even more awful to consider that humans created bombs when they were given a plentiful world in which to live.

Based on the advice of scientists and radiation readings, the citizens of Melbourne know when the radiation will reach their city and, therefore, know when they will die. This knowledge causes pain and internal conflict for the people. Even those who have not accepted the news put mental effort into the denial process, struggling between accepting and disbelieving their inevitable fate. Peter and Mary spend time planning their garden for the next ten years, but then, just a few days later, Peter talks to the pharmacist about cyanide for his wife and daughter. Peter battles between being strong enough to face the reality and optimistic enough to hold onto hope. Moira's father undergoes a similar struggle. He reminds Mrs. Davidson that Moira will not have time to start a family, but at the same time, he continues to fertilize his pasture and prepare his farm for the next year. Even the military and government have not given up hope yet. They are sending the submarine all the way to Alaska to investigate the Jorgensen theory, desperately hoping it to be true. The military is also hoping that the radio signals coming from Seattle indicate someone is still alive in the Northern Hemisphere. Although the signals are incoherent and the chances of finding someone alive are slim, the government nonetheless clings to that hope.

It seems that no one believes they are going to get sick until the symptoms actually start to show. When Dwight and Mr. Davidson discuss the lack of refugees in Melbourne, Moira's father provides the most plausible explanation: people have not come south because they never believed the radiation would actually get them until they were already sick. Suggestions that the Prime Minister's speech over the radio calmed people and convinced them to stay in the radiated areas seems less plausible than the fact that people simply did not believe they were going to die.