John Gunther (hereafter referred to as Gunther) writes that this memoir is about death and what his son Johnny courageously endured, in an effort to provide hope to others who have to deal with similar pain. Gunther briefly sketches Johnny's life: he lived in Vienna and London when he was young; attended Deerfield Academy in Massachusetts; and died in 1947 at the age of seventeen, after a fifteen-month-long illness. He describes Johnny's adolescent but handsome appearance, his amiable nature, his tremendous willpower, and, above all, his selflessness. He notes Johnny's varied interests, his incredible intelligence, and his passion for science. He also mentions his ex-wife, Frances, with whom Johnny is very close.

Johnny returns home for Spring break and has a good time. The family doctor, Traeger, says that he's fine. However, he does have a slightly stiff neck. At school, they believe Johnny has a brain tumor, so they bring in a specialist, Tracy Putnam. Gunther and Frances drive to Deerfield, and when Gunther sees the face of one of the doctors, he immediately knows that Johnny will die. Johnny endures a painful spinal tap and is sent by ambulance to Columbia- Presbyterian Hospital in New York. He manages to stay upbeat and intellectual about his worsening condition. He has his first operation on April 29, which takes six hours. Johnny's tumor is in a difficult spot for extrication. The operation removes half of the orange-sized tumor. Johnny makes a fast recovery, and he is walking within two weeks and exhibiting his normal curious intellect. On May 28, Johnny faints and gets worse. Gunther finds out the tumor is undergoing glioblastomatous transformation, a far worse condition that carries the possibilities of blindness, paralysis, and the inevitability of death.

Johnny is discharged from the hospital on June 1, but he continues going every day for x-rays until June 20, when he returns home to Connecticut. His physical activity is restricted, but he busies himself with his science workshop in the garage and with visits from friends and relatives. Johnny develops papilledema, a protrusion that damages the optic nerve and loses a great deal of peripheral vision. The bump on his head opens and leaks pus. He is taken to Wilder Penfield, a renowned surgeon. Penfield tells Gunther that the tumor will kill Johnny. Frances reads a newspaper article about how an experimental method of intravenous dosages of mustard gas, which is commonly poisonous, can improve tumors. Memorial Hospital in New York administers its first injection of mustard gas to Johnny. The mustard produces bad side effects, but it helps Johnny at first. He returns to the country and devotes himself to making up his lost schoolwork and other activities. On August 31, another leak develops. Gunther learns of Max Gerson, a doctor whose unorthodox methods of treating illnesses are based on a controversial diet. With nothing to lose, he and Frances decide to put Johnny on the diet. On September 7, they drive to Gerson's nursing home.

At Gerson's nursing home, Johnny starts feeling better. Traeger agrees to continue with Gerson's methods, which include rest, daily enemas, and a salt- free, fat-free diet. Johnny gets much better, and Gunther is confident that he will fully recover. Frances keeps Johnny in high spirits, reading to him and bringing gifts. Johnny's bump worsens, and he develops a second bump. When Gunther tells him he cannot return to school, he furiously makes up his lost time through tutoring. He writes a letter to his headmaster, asking for a reprieve from his unfinished work and another letter to his math teacher, asking to take an important algebra exam. Johnny worsens, though his doctors are amazed that he is still alive. They fight about whether he should undergo more drainage. Gunther and Frances decide on a compromise, which includes surgery while keeping with the Gerson diet. Johnny heads off to the Neurological Hospital for five weeks. Dr. Mount makes a highly successful emergency drainage. Johnny's recovery is strengthened, the bump disappears, and everyone believes he will be back to normal within a year, especially when they find out the pus from his bump was sterile, indicating that the tumor is dead. He returns home on February 6 for the first time since August.

In early February 1947, Johnny is physically stronger. By late February, however, the bump grows again. He exhibits the first of a series of short-term amnesia attacks on Feb. 19. Johnny wants to get off the Gerson diet and return to Deerfield, but both requests are denied. He works hard to make up his schoolwork in preparation for Harvard, and he enrolls and excels in a tutoring school. On April 12, he takes his college boards. Gunther finishes the book he was writing, and he takes Johnny to Neurological Hospital for an exam. Mount takes some fluid as a sample but is only able to extract very little from the stone-sized, rigid structure. Gunther is told Johnny has glioma multiforme, one of the worst forms of tumor, and it is rapidly worsening. Penfield urges Gunther to have him undergo a drastic second operation to try and clear out the tumor. They decide to take him off the Gerson diet. On May 1, Mount extracts "two handfuls" from the tumor, but the tumor is still huge.

Johnny's bulge disappears and is replaced by a long-awaited concavity. On May 15, he is checked out of Neurological Hospital. On May 25, Mr. Boydon, the headmaster of Deerfield, calls and announces Johnny will receive his diploma because of his extra credits. They drive to Deerfield. Johnny attends all the graduation events and, on June 4, he marches to get his diploma despite his ill health. They repeat Johnny's earlier treatment—mustard gas, x-ray, Gerson diet, and possibly another operation, in that order of increasing intensity. On June 12, Johnny is sent back to Memorial Hospital. On June 27, Johnny suffers a worse attack of amnesia and the shivers. Johnny maintains his drive for Harvard, even though he has difficulty feeding himself, and his shiver attacks seem permanent. Frances visits on a Sunday, and on this day, Johnny regains his energy, enjoying a wonderful day with both parents. The next day, June 30, Johnny is fatigued. Gunther takes him to Memorial Hospital for a last test before he heads to the country. At home, Johnny has a bad headache, and morphine is sent to the house after he vomits a caffeine pill. Johnny grows hazier and Gunther calls Traeger to come over. Traeger tells Gunther that Johnny is dying from a cerebral hemorrhage. After several complications, they transport him to a nearby hospital. There, he is given extensive medical attention, but it is not enough. Johnny goes to sleep and never wakes, dying at 11:02 P.M.

Gunther transcribes the letters Johnny wrote in his life from age seven until near his death. Johnny's early letters display his sensitive, loving side, and his fascination with science and a variety of hobbies that he would take with him throughout his life. His last letter, to Frances, includes a scribbled note: "Scientists will save us all."

Gunther also transcribes a diary that Johnny kept over the last few years; Johnny took the notebook with him wherever he was while sick. Since Johnny left the diary conspicuously in the open, Gunther and Frances believed he was using it indirectly to communicate to them thoughts he did not want to discuss. One entry lists the five-part "Gunther philosophy," which includes rules and reminders like the Confucian Golden Rule (do unto others as they would do unto you) and "No immortality." His post-tumor entries rarely touch upon his condition, but they continue with philosophical ruminations and directions, academic reports, and day-to-day news, though he occasionally exposes his fears and turbulent emotions.

Frances narrates the final section. She brings up all the questions about life that death raises, which she says she discussed with Johnny throughout his illness; to her, he was not merely dying, he was re-born each day. The only answer she can muster to all the philosophical questions is that she wishes they had loved Johnny more. She wants to tell other parents to embrace their children, who are alive, not dead. She resolves again that the aim of life is to love, to eradicate hate, and that she hopes to love Johnny more and more until she dies—as that kind of love is a "love of love, the love of life."