While trying to find a new best friend after feuding with Rowley, middle-school slacker Greg Heffley is warned by older family members that adolescence is a time to act more responsibly and to think seriously about his future.

“Tất nhiên, một ngày tôi sẽ nổi tiếng, nhưng than ôi, bây giờ tôi đang bị mắc kẹt ở trường với một lũ trẻ con ngốc không để đâu cho hết”. Hơn bất cứ ai, chú bé Greg Hefley biết rõ rằng làm một cậu nhóc thật vô cùng phiền toái. Cậu nhận ra mình đang bị mắc kẹt ở trường trung học, nơi những đứa trẻ yếu ớt lúc nào cũng phải đi chung hành...

"Secrets have a way of getting out, especially when a diary is involved. Whatever you do, don't ask Greg Heffley how he spent his summer vacation, because he definitely doesn't want to talk about it. As Greg enters the new school year, he's eager to put the past three months, and one event in particular, behind him. Unfortunately for Greg, his older brother, Rodrick, knows all about the incident Greg wants to keep under wraps. But secrets have a way...