Fudge-a-Mania by Judy Blume focuses on Peter Hatcher, a fifth grade boy from New York City. He must share a vacation house in Maine with his arch enemy, Sheila Tubman. Peter must come to terms with the beginning of adolescence by dealing with Sheila and his pest of a little brother, Fudge.

Peter Hatcher is a fifth grade boy from New York City. His mother tells him that the family is going on a three week vacation to Maine. She says that they will be neighbors with Sheila Tubman's family. Sheila is Peter's arch enemy. She is in sixth grade and he cannot stand her. Mom tries to ease the shock by saying Peter can invite his friend, Jimmy. Peter tells Jimmy that his house and Sheila's house are far away and they will not have to deal with her. Jimmy agrees to come. Peter dreads the vacation.

Peter's family drives 10 hours to Southwest Harbor, Maine, a cute, little town. When they pull up to the vacation house, Sheila is on the porch. Peter realizes his family and the Tubmans share a connecting house. They must share a kitchen and living room. Only a door separates their two living spaces. Peter is horrified. Sheila is not happy either because she hates him too.

Sheila gets a job babysitting Peter's five year-old brother, Fudge. Fudge is a curious and energetic boy. He is a handful. Since Jimmy is not there for the first part of Peter's vacation, Peter must hang out with Sheila and Fudge. They meet Mitzi, who is a neighbor girl and Fudge's age. Mitzi's grandfather is Big Apfel, who was a star baseball player for the Boston Red Sox. Peter gets excited that he will get to play in a Sunday game that is hosted by Big.

Jimmy visits. He is nice to Sheila, which makes Peter angry. Peter is angry because Jimmy is his friend, not Sheila's friend. Peter also develops his first crush on the library assistant, a 16 year-old girl who is pretty. Sheila and Fudge tease him about it.

They play in the baseball game with Big Apfel. Peter hopes Big looks at him and loses his concentration. He messes up a lot. He begins to get angry at himself, but Jimmy thanks him for inviting him to play. Fudge says Peter is his best brother. Peter realizes some things are more important than the baseball game like being a good friend and brother. Peter's grandmother and Sheila's grandfather have a romantic relationship and they marry. Peter realizes he will never get away from Sheila. During the reception, Peter and Sheila agree to hate each other forever.