The following version of the book was used to create this study guide: Blume, Judy. Tales of a Fourth Grade Nothing. Penguin Young Readers Group, New York, New York, 1972. Kindle AZW file.

Peter Hatcher is nine years old and lives in an older apartment building in New York City with his parents and his younger brother Farley, whom everyone calls Fudge. Peter feels sorry for Fudge because of the nickname. However, sometimes, he also feels jealousy toward Fudge for all the attention he gets and anger that Fudge wrecks so many things in Peter's life without facing any consequences.

Two of Peter's fellow students live in his apartment building. Peter and Jimmy often spend time in nearby Central Park where they like to play on a particular rock. A girl named Sheila sometimes interrupts their play and chases them with threats of “cooties.” One day, Sheila, Peter, and Jimmy are in the park when Mrs. Hatcher walks by with Fudge. Sheila begs to babysit him, and Mrs. Hatcher agrees that all three of the children can watch Fudge while she runs back home, promising to be back in a few minutes. While the three older children are playing, Fudge climbs to the top of a piece of playground equipment, pretends to be a bird, and jumps. He knocks out his two front teeth, prompting a trip to the dentist and making Peter suggest they call him Fang instead of Fudge. Mrs. Hatcher does not find it funny and insists Peter drop it.

Most of the time, Fudge's antics result in damage to someone or something at home. One day, he draws all over Peter's project for school, forcing him to start over. Peter is surprised that his mother spanks Fudge. Mr. and Mrs. Hatcher warn Fudge to stay out of Peter's room. After that episode, they also install a sliding lock that is out of Fudge's reach. A few days later, Peter arrives home to find that Fudge has unlocked the door anyway and his turtle is missing. Fudge happily explains that he ate the turtle. Mrs. Hatcher rushes him to the hospital where the doctor confirms the turtle is in Fudge's tummy. They give him doses of castor oil and keep him for two days, waiting for the turtle to pass through his system.

Peter is horrified that everyone is worried about Fudge and no one seems to remember that Peter's turtle died because of Fudge's action. Peter becomes so angry that he wishes Fudge was not part of the family. When his parents arrive home from the hospital with Fudge, the youngster has several presents he got while he was hospitalized. Peter's anger grows that Fudge has been rewarded while Peter no longer has his pet. When Mr. Hatcher presents Peter with a gift, Peter expects a turtle and makes it plain he does not want a replacement. Inside the large box, Peter finds a puppy. Mr. Hatcher assures Peter that this is his dog, a reward for being understanding about the recent situation. He also assures Peter that the dog will grow. There is no danger of Fudge swallowing it.