The Third Wheel
The book starts with the cute and sweet Greg talking about what his life was like before he was born. He describes life in his mother's belly, where she attempts to make him smarter by playing classical music and reading him books. She fails. After being forced to hear his mother's gross secrets and having to deal with listening to his parents smooching, Greg decides to get out of there, explaining why he was born three weeks early, a decision he soon regrets.
In his toddler years, Greg tells the reader that his family originally lived in a small apartment, and he had to sleep illegally in the top dresser drawer. All of his own stuff are hand-me-downs from Rodrick, as his parents are too poor. Later on, the family moves to a different house, where Greg and Rodrick have more space. His mom attempts to get Greg smarter by watching educational videos, but fails once again because Greg keeps stashing the remote battery in his diapers.
Then Greg gets a new baby brother (Manny).
In preschool, Greg realizes his classmates are way ahead of him and that he can't catch up, so he tries to slow them down by feeding them bad information. The teacher informs Susan of what he's doing, and Susan believes Greg is not challenged enough, and moves him to kindergarten. It does not work out well, and Greg ends up dropping out of from kindergarten back to preschool.
Then Greg explains some of the parenting methods his mother has tried on Manny and how Manny has been affected by those methods, which are very different from what Greg's mother did with him.
Meanwhile, back in present day, Uncle Gary moves into Greg's house, causing the family great disturbance and annoyance. He explains he got a great deal from T-Shirt shop owner in Boston to take over his business, but the shirts have typos on them.
In school, Rowley Jefferson, Greg's friend gets elected Social Chairperson, getting him on the Dance Committee for the Valentine's Day Dance. Greg tells Rowley to find him a date, and eventually Rowley tells Greg about a girl called Abigail Brown, who is alone after her boyfriend, Michael Sampson, had some family obligations. Greg asks Rowley to ask Abigail to go with them as a group of friends; she agrees. Greg's idea is to use Rowley to get him a girlfriend, so he can go on a date with her.
At the dance, their night is ruined when senior citizens overrun their dance, claiming they reserved the dance area first, but they compromise things that ruin the theme. Finally, while dancing with Abigail, Greg spots what looks like chicken pox marks on her face. After witnessing Rowley's pimples earlier on, which he mistakes for chicken pox, Greg panics, leaving Abigail crying and Rowley comforting her. The book ends with Uncle Gary winning forty-thousand dollars and paying off his debt to Greg's Dad which was created in the past, He then moved away to another place. Rowley and Abigail are dating, and Greg gets the chicken pox.