John, the narrator of Cat's Cradle, began to write a book, titled The Day the World Ended, about the day the atomic bomb was dropped on Hiroshima. At that time, he was a Christian, but now he is a Bokononist. Bokononists believe that all of humanity is organized into teams, called karasses, that unknowingly carry out God's will. Bokonon, the founder of the religion, warns that attempts to discover the purpose of one's karass are destined to yield incomplete knowledge.
The Books of Bokonon open with a warning that everything contained within is composed of "shameless lies." John warns that anyone who cannot understand that a useful religion can be built on lies will not appreciate Cat's Cradle. John's other book, now left unfinished, led him to his karass, which includes Angela, Frank, and Newt Hoenikker, the three children of the Nobel-prize-winning physicist Felix Hoenikker, one of the scientists who invented the atomic bomb. Long ago, John wrote to Newt, who was then a medical student at Cornell. In the letter, John asked Newt what he remembered of the day the bomb was dropped on Hiroshima.
Newt replied to John's letter, stating that he was only six years old that day. He was playing with his toy trucks in his home in Ilium, New York, and his father was playing cat's cradle with a piece of string. Usually, Felix had no interest in games invented by other people. He was once quoted in Time magazine as saying that since there were so many "real games," the made-up ones never interested him.
Rather randomly, a prisoner had mailed a manuscript of a book he had written about the end of the world to Felix; the prisoner wanted technical information about a theoretical bomb that might be able to kill all humanity. Felix never read the book, but he was fascinated with the string tied about the manuscript. He hardly ever took interest in books or people, even his own family, yet that morning he went to Newt to show him how to play cat's cradle. As he approached Newt, Felix looked so huge and ugly that Newt burst into tears and fled the house. Angela has since told Newt many times that his reaction hurt his father's feelings, but Newt thinks he couldn't have hurt him much since Felix took so little interest in people. Felix didn't even remember much about Emily, Newt's mother, after she died.
Newt ran out to sit with Frank, who was 12 years old at the time. Frank was occupied with Mason jars full of bugs, which he shook to make the bugs fight against one another. When Angela, who was 22 at the time, asked him what he was doing, Frank replied that he was "experimenting." She asked Newt why he had run from Felix, and Newt told her that Felix was ugly and frightening. Angela slapped Newt, and, in response, Frank punched her in the stomach. Angela called for Felix. Frank laughed, correctly predicting that Felix would not respond to her call.
When he was working on the bomb, Felix became fascinated with turtles. He quit working on the Manhattan project to investigate this new interest. Angela advised the other people involved with the project to simply remove the turtles from his laboratory if they wanted to direct his attention back to the atomic bomb. When Felix found nothing in his laboratory to "play with and think about" except the atomic bomb research, he promptly began working on it again. The day the bomb was tested, another scientist told Felix that science had finally encountered sin, but Felix merely asked what sin was.