Diary of a Wimpy Kid: Dog Days is all about Greg’s BAD summer. It first began when Greg and Rowley went to a country club, and Rowley’s dad got mad when they wrote his credit card when they’re gonna buy a smoothie. It turns out they bought and bought many smoothies, and they all cost $83.00. So both of them need to gain $83.00 and pay them to Mr. Jefferson. The job they did to pay their bills was a lawn care service. But they can only make one flyer after Mr. Jefferson told them they cannot use his computer. Unfortunately, the job ended as a fiasco when the boys never used a lawn mower before, all the gas leaks out of the mower, and the instructions are in Spanish. When Greg tells Rowley he has to do most of the work while Greg counts the money, that made Rowley annoyed and he quits.
The beach trip that he was looking forward to with his family is canceled because the Heffleys don’t have any money. So what he ended up was in a town pool which he dislikes because of its open showers showing large, hairy men.
Later, Greg and Rowley have a sleepover together, and watch a horror movie taken from Rodrick’s room. After the movie, Greg and Rowley soon became paranoid on account of a muddy hand that might kill them, which was in the movie. Unfortunately for Greg, his mother knew that he and Rowley watched the horror movie, which Greg and Rowley shouldn’t watch. Greg’s father told her mother when he found them sleeping in the bathroom, which is why he knew. So she decided to start a reading club. First there were tons of participants. Then many left the club and there were only 2 left, which is Greg and Rowley. And the next day, Greg is the only one left in the club. So his mother put the club into a stop when she knew that they still haven’t paid their bills from the smoothies they bought.
Then, Greg’s birthday arrived, but the gifts he received are all useless for him, including a useless cellphone that only calls home and 911. Greg gets money in every birthday card he receives, but his mother confiscated it to pay off his $83.00 from Mr. Jefferson. Greg’s birthday was ruined when his uncle’s dog, Killer, almost ate his cake.
Then it’s Father’s Day, so his family visit Leisure Towers to spend the day with Greg’s grandfather. There, his father tells of how his dog, Nutty, ran away to a butterfly farm. Greg’s grandfather then explains that he had actually run the dog over and Greg’s father got annoyed by it. So he bought a dog which Greg’s mother names it “Sweetheart” or “Sweetie”, even though the dog is male. Even though Greg has wanted a dog for a long time, he quickly becomes annoyed at Sweetie because he ruins his time almost everyday.
The Jeffersons later invited Greg to go to the beach with them, which is where Greg had wanted to go, but he realises it wasn’t what he expected, where he begins to have a breakdown from no electronics, almost got jumped by teenagers he pulled a prank on, and especially the Cranium Shaker, which almost makes Greg vomit.
Greg’s mother tries to get Greg and his dad together, but both of them realized that they should keep their distance. However, they both hate much of the same things, such as a comic named Li’l Cutie, where the writer has retired and passed it on to his son (who was possibly the basis of the character when he was little) and has made the comic even worse.
The book ends when Greg realized that summer is over when he sees his mom’s photo album titled “Best Summer Ever!”. But actually it is a “horrible record” of that summer to Greg.