The book opens with the sudden dropping of the atomic bomb on the Japanese city of Hiroshima on August 6, 1945. The narrative then follows six survivors of the blast as they recount their lives before, during, and after the explosion.
The first person, Reverend Kiyoshi Tanimoto, is a beloved priest. On August 6, he wakes up early to help his friend move some heavy furniture to another house. At 8:15 am, while Tanimoto and his friend are outside the house, a bright light flashes across the sky, and the force of the explosion throws Tanimoto to the ground. However, because he is miles away from the blast center, he survives without any serious injuries. Another woman living in Hiroshima, Hatsuyo Nakamura, wakes up very early on August 6. Nakamura is a widow who sews for a living. When the bomb explodes, Nakamura’s house is reduced to rubble. She is able to crawl through the rubble and save her three young children.
Another Hiroshiman, Dr. Masakazu Fujii, is sitting on the porch behind his home (which doubles as a single-practice hospital), reading the paper. The force of the explosion rips the porch out from the building and throws it into the river below. Fujii is able to wade out of the river, though he has broken his collarbone in the fall. A German priest living in Hiroshima, Father Wilhelm Kleinsorge, is sitting in his chapel during the blast. The young doctor Terufumi Sasaki is working in the Red Cross Hospital when the explosion rips apart some of the building’s walls. Sasaki is uninjured, and he immediately begins tending to the victims of the explosion. The final main character in the book, a young clerk named Toshiko Sasaki, is sitting in her office; in the explosion she is crushed under a heavy bookcase, so that “in the first moment of the atomic age, a human being was crushed by books.”
In the chaos following the explosion, Tanimoto runs back into the center of the city, desperate to find his wife, child, and church congregants. Almost miraculously, he is able to find his family, even though tens of thousands of people who haven’t been killed are running through the streets. However, when he sees his wife, Tanimoto doesn’t say much to her; he just nods, explains that he wants to check on his church, and runs off. Around the same time, Father Kleinsorge and the other uninjured priests at his church run through the neighborhood, helping people from under their wrecked houses. Dr. Fujii also risks his own safety to help some of his neighbors. Nakamura gathers her three children, all of whom are uninjured, and leads them toward nearby Asano Park, where Hiroshimans have been instructed to gather in times of emergency. By this time, fires are breaking out across Hiroshima; the heat of the nuclear blast has been so intense that it is now destroying the city’s remaining buildings, most of which are made from wood. Dr. Sasaki continues working hard in the hospital, while Toshiko Sasaki remains trapped under the bookshelf for hours. Eventually, two men free her and take her to the courtyard of her building, where she lies next to two other injured people for the next two days, without any food or water.
Many of the surviving people of Hiroshima gather in Asano Park. Father Kleinsorge and Reverend Tanimoto are both there, tending to the injured and dying and fetching buckets of water for them from the nearby river. Tanimoto finds a small boat, which he takes regretfully from its dead owners, and he uses it to transport injured people up the river toward a Novitiate chapel outside the city. There, some of the priests, who’ve been trained in medicine, are able to give the Hiroshimans medical care. On August 15, Emperor Hirohito officially declares that Japan is surrendering to the United States.
Within a few weeks of the bombing, it becomes painfully clear that many of the Hiroshimans who survived the bombing are suffering from a rare disease: radiation sickness. One of Mrs. Nakamura’s children feels tired all the time, and Father Kleinsorge has so little energy that he has to go to the hospital. Japanese scientists have had some previous experience dealing with radiation sickness (mostly from people who’ve been exposed to too many X-rays), though never on this scale. In addition to having a child suffering from radiation sickness, Mrs. Nakamura loses her only source of income, her sewing machine, in the explosion. Dr. Fujii loses his hospital, Kleinsorge and Tanimoto lose their churches, Dr. Sasaki is severely traumatized by the explosion, and Toshiko Sasaki is severely injured. In other words, six of the luckiest people in Hiroshima on August 6, 1945 are still devastated by the events of the day.
In the long final chapter of the book, written forty years after the bombing, Hersey traces the lives of his six main characters. Mrs. Nakamura becomes a typical hibakusha (Hiroshima survivor). She struggles to support herself, is shunned and even harassed by others, and, for many years, is utterly ignored by the Japanese government. She works in a chemical factory to support her children, but benefits from a 1957 law providing her with financial and medical compensation. Dr. Terufumi Sasaki goes on to become a highly successful doctor; however, Hersey suggests that he throws himself into his work as a means of forgetting about the past. Father Kleinsorge remains in Japan for the rest of his life. He suffers from weariness and exhaustion brought on by his radiation poisoning, but he devotes himself to teaching the Bible to children and giving comfort to the sick and dying until his own death in 1977.
Toshiko Sasaki experiences an incredible transformation following the Hiroshima bombing. Father Kleinsorge visits her in the hospital and gradually converts her to Catholicism. After leaving the hospital, Sasaki becomes a nun, and eventually rises to become Mother Superior of her convent. In 1980, she is honored with a dinner celebrating her twenty-five years of faith. Dr. Fujii continues to live a successful, prosperous life; however, it’s likely that he suffers from depression brought about by the bombing. In 1964, he is found asleep in his room with the gas heater turned up all the way, suggesting that he was trying to kill himself. Fujii spends the last eleven years of his life vegetative in a hospital.
Reverend Tanimoto spends the second half of his life campaigning for a variety of pacifist causes. He raises money in the United States for his church and for the establishment of a World Peace Center in Hiroshima. However, Tanimoto lacks any real influence in the Japanese government; he is a talented fundraiser, but he can’t influence any concrete policies in his own country. Tanimoto also finds it difficult to assimilate with the anti-nuclear movement in his country, which is dominated by far-left radicals and secularists. Year after year, the powerful countries of the world continue to experiment with nuclear weapons and expand their nuclear arsenals. In the 1980s, a poll finds that most hibakusha believe that nuclear weapons would one day be used again in war. Meanwhile, the Soviet Union and the United States stockpile nuclear missiles—suggesting that another nuclear conflict is likely, and that the world’s memory of the horrors of Hiroshima “is getting short.”