The Scorpion has left on its voyage to North America. After twenty-five straight days submerged to avoid the radiation, Dwight is worried about the mental health of his crew. To relieve tension, he lets them use the periscope to look at the western coast of America, the home country of most of the crew.
One of the primary objectives of the mission is to investigate the mysterious radio signals coming from the Seattle area. The crew hypothesizes that the radio transmitter is running off of hydroelectric power—common in the Pacific Northwest—but they do not know who or what is sending the incoherent messages. They soon discover the signals are coming from Santa Maria Island, just as Lieutenant Sunderstrom predicted. Dwight will send Sunderstrom the next day to the island to investigate. Before Dwight sleeps that night, he looks at the bracelet for his wife and places the fishing rod for his son by his side.
In the morning, the submarine surfaces near Edmonds, a small town close to Seattle. Even though the radiation level is high enough to kill all life, everything in the town looks normal. The crew uses a loudspeaker to see if anyone is left alive onshore, but they get no response. The sub's radar operator, Yeoman Swain is from Edmonds; Dwight invites the young man to look at his hometown through the periscope. When nobody is looking, Swain escapes through a hatch, jumps ship, and swims to shore. Dwight tries to hail Swain, but he refuses to return. Swain will only have a few days left to live, but it will be too dangerous to take him back onboard if he stays in the radiated area for more than a few hours.
The submarine moves on to Santa Maria Island. Lieutenant Sunderstrom puts on a protective suit and takes a small boat to shore. He has less than two hours to discover the transmitter and its electrical source. On shore, he discovers a decomposing body. Sunderstrom finds the converter that provides electricity to the transmitter, and he then finds the transmitter itself. It turns out that a broken window frame has fallen out of the window and is resting in an unstable position on the transmitting key. When the wind blows, the window frame rocks on the transmitting key and sends a message.
Sunderstrom moves the window frame away the keys, and then transmits a message in Morse code saying that the submarine is safe, but that there is no life on land. He returns to the electric converter, admiring the machine before turning it off; he would feel bad letting it stay on until it simply wore out. On his way out, he finds a stack of issues of the Saturday Evening Post and decides to take the magazines with him.
As Sunderstrom is walking back to shore, he comes across a group of people sitting in lawn chairs, having drinks on a verandah facing the water. He begins to approach, but then realizes in horror that the people are all dead, and have likely been so for about a year. The submarine turns back and comes across Yeoman Swain fishing from a motorboat. He reports that he has found his family and girlfriend dead, but that he is happy because he is home and because he has his car and motorboat.
The military in Australia receives the radio signal that those aboard the submarine are alive. Mary calls Moira to share the news that the crew is safe, and Moira almost faints from relief. They meet each other and talk about how crazy it is to garden or learn shorthand under the circumstances. Moira says that because of Dwight's influence she does not drink as much as she used to. She would want to marry him, but he still thinks he is going home to his family in September. Normally, Moira would use every dirty trick imaginable to get him, but not when there is only a few more months left to live. Mary cries when she tells Moira about Peter's instructions that she use the syringe on Jennifer if the baby gets sick.
The submarine returns to Melbourne and reports the disappointing news that they had disproved the Jorgensen effect—precipitation has not cleared the air of radiation in any area they have visited. Dwight receives a message informing him he is now the Commanding Officer of the United States Naval Forces. The previous Commander has apparently died from radiation, which has reached Brisbane; he refused to abandon his crew and move south on his own. Dwight tries to radio Brisbane, but finds that he is no longer to make contact with anyone there anymore.
Millions of people have died in the war, but we do not see a single dead body until this chapter. Although Shute could easily be more graphic, his writing is restrained as he describes the decomposing bodies Sunderstrom encounters onshore. In fact, the lack of detail is in a sense more terrifying than specific descriptions. Shute does not have to say that radiation sickness forced people to spend their last days throwing up or suffering from diarrhea. He merely hints at the messy deaths by saying that Sunderstrom comes across a body sprawled out of a latrine. The suspense is especially palpable when Sunderstrom comes across the group of people sitting on the verandah; it is left to us to imagine the horror the soldier feels.
The scene with Sunderstrom and the window frame resting on the transmitter is almost comic. He looks at the window frame and thinks that it "was not damaged and could be repaired and put back in place quite easily." He is feeling a need to fix the unfixable. Even when he is surrounded by death and destruction, it is surprising that Sunderstrom still has time to admire the transmitters sending the messages. He even goes as far as to look for the name of the manufacturer of the equipment. He hates the idea of the machine wearing out and breaking, so he turns it off, giving it a more humane death than that experienced by most of the war victims. Though such efficient, anonymous machines have led to the destruction of humanity, Sunderstrom, like many other characters in the novel, is still in awe of such gadgetry. Yeoman Swain also cannot resist the charm of machines: even though he has just found all his loved ones dead, he is still happy because he has a car and a motorboat. He has cared so much about everyday technology that now machines are his final companions. Although such a sentiment is ironic, Shute does not mock humanity's love for their machines; he merely states that this love exists.
Back in Australia, we see that Moira is growing up, that she is doing so more quickly than she would have liked. Although she insists she does not do anything restful, Moira is finding peace with her situation. She, too, has turned to work as salvation. She knows sin and trouble too well, but she has not become bitter. She knows sorrow, but she has not become sad. Even with the knowledge that she will die soon, she displays a determination to make the best of herself in this situation. While Mary makes no attempt to face reality, Moira is now brave and honest enough to admit that everyone is "all going mad in our own way." Shute likes to write about decent, honest and principled people; here, he lets Moira grow into a person whom anyone could admire.