It tells the story of Swedish fifth-grader Bert Ljung during the spring term from 14 January to 4 June the year he turns 12.

Må han brinna i fasans eld i all evighet... eller i varje fall en liten stund.translated: Death to the one who reads this diary in secret.

May he burn in the fires of Hell forever... or at least for a short time.Berts dagbok is set during the spring term in the 5th grade, and runs from 14 January to 4 June.

Bert and Åke also invent their own fictional country, Hoppalotjingien, which later in the book ceases to exist following a "civil war".

During Bert's 12th birthday party in late February, Klimpen tricks him into smacking Rebecka's butt with a rubber snake, and she walks home.

During a Friday evening school dance event in May, Bert falls in love with Nadja Nilsson in class 5E at Jungberska skolan.

Torleif tells Bert that she plays the violin in the same orchestra, and that she lives near the soccer ground in a little cottage with her mother and three brothers.

The book ends with Bert and Nadja meeting in the town park on 4 June under an old oak tree, and on its trunk, they carve their initials (NN + BL).

The 1993 reissue opens with a review of class 5A at Beckaskolan, and it is here Bert's schoolteacher's name (Sonja Ek) is mentioned for the first time; she was previously referred to as fröken ("Miss").

[5] The story where Bert's myopia is discovered, leading to him getting glasses and getting teased by Klimpen, also appears in the episode "Den ohyggligt fule" of the TV series.

The 1993 reissue also includes a school discothèque with a masquerade ball, which has become famous and appears in the TV series episode "Min älskling, du är som en tulipan" and the comics.