The Christmas-New Year holiday season goes towards its end, and Bert writes in his new diary. When Åke returns home from a holiday to the Canary Islands, the pop/rock band Heman Hunters (which has been required to change name from "Dum i huvet" ("Stupid in the head") as the old band name gave no gigs) meets at Åke, and here the band gets its recurring line-up. Soon, the spring term in the 6th grade begins.
Bert is still together with Nadja, but when a new guy in his class appears, she tells him he "looks pretty good". During a break-in at the Beckaskolan school canteen, Bert believes/hopes the new guy in Nadja's class did the break-in, before Nadja tells that a 56 years old man did the break in. When Bert goes to Nadja, her raggare, brothers forces him to do a "raggare PRYO ".
In January, Bert's neighbour "kapten" ("captain") dies when his favourite bandy team loses an important televised game, and the municipality responses for the funeral as he has no relatives still alive. Bert and Åke decide to attend the funeral and read a poem.
When the king of Sweden has his name day on 28 January Bert and Åke set up fireworks for him in the park, using Åke's home-made fireworks, who fly away in a one-way direction towards a house. When Bert visits Nadja, he puts cotton balls in her ear to avoid hearing her playing the violin, which turns her angry and she fights with the violin bow, which hits the cotton ball in Bert's ear.
In late January, Bert's father tries to get Bert's family into dieting, but some days later it all ends when his mother finds sausage on his father 's necktie when he has been out dining with work.
In February, Bert tricks his grandmother to call "Heta linjen" when his parents travel to Åland. When Bert is about to turn 13 on 21 February, he and Åke start longing for moped, two years before the laws of Sweden would allow them to drive one. However, they manage to borrow mopeds from a lessor. Bert also pawns his father's wedding ring, but regrets his acting when noticing Ågren, who he believes has been sent out by God, and Bert purchase the wedding ring again, despite it being more expensive this time. As Bert turns 13 he receives a greeting hug from Paulina in class 6 B, and his interest for Nadja slowly starts to decline. During Bert's birthday party, which Nadja doesn't attend, Björna invites Bert's mother for a dance (which Lill-Erik mimics some days later by borrowing Bert's mother's bra), and Torleifs recorder flute breaks apart as Bert's mother locks it up in the refrigerator.
On 1 March Bert goes to Nadja and breaks up with her, and soon shows his interest in Paulina. The guys in Bert's class hold a "penis measuring contest" in March, which Bert wins when he starts thinking of Paulina. As optional subject for the 7th grade, Bert chooses media, which Paulina also does. Bert also accidentally tells Paulina he has a dog, when she tells him she likes dogs. However, Bert has no dog, and is parents are allergic. An attempt to make Lill-Eriks dachshund look like a poodle fails.
Bert also receives new neighbours, as Italian immigrant family Panatta from Sundsvall moves into recently deceased neighbour Kapten's former apartment, and a party is held.
In April, Bert does his PRAO at the "Kurres bensin & tillbehör" petrol station, even if he wanted to do it at the fire station, a place that Jörgen Karlsson takes. The guys in Bert's class use Björna's drill to drill a whole in the girls physical education changing room. Bert still likes Paulina, and wishes he had a secret telephone line over to class 6 B, as he knows Paulina does well at school, and could have help him during homework tests.
During a wild school dance (where a 7th grade girl shows the guard her breast) at Jungbergska skolan, Bert learns that Paulina's mother is actually a cousin to Nadja's father.
Bert also fixes a practice hall for the Heman Hunters, located in the basement of the apartment building where Bert's family lives. The neighbours first think the noise coming from the basement are abuse, and the ambulance and the police appears, before the band sings for the rescue staff.
The book ends with an image of a pencil, and the words:
"Detta är den penna i naturlig storlek, med vilken dessa betraktelser nedtecknats."
translated
"This is a pencil out of natural size, with which these contemplations have been written down"