Madelief is looking for her cat Tamara. When she finds it, it stars climbing the curtains, but Madelief manages to pull it down. When Tamara bites Roos and scratches Madelief, the children start telling each other increasingly taller tales of gruesome accidents they say they have been in.

Jan-Willem thinks he is being rebuked by his mother for talking dirty, but in fact she just wants him to do some last-minute shopping for her. In the big supermarket, Jan-Willem feels lost and intimidated by the staff. As he result, he doesn't know what to buy.

In the park, a large, terrifying dog grabs Jan-Willem's ball. But when three older bullies kidnap Jan-Willem later on, Madelief and Roos come up with a plan to rescue him by tricking the dog into helping them.

While Madelief and Roos are watching a German crime series on TV, Jan-Willem sees a strange submarine emerge in his aquarium. The girls are so engrossed in the thrilling program, that they fail to pay attention to the even bigger mystery right at home.

Jan-Willem's mother wants to buy her son a smart suit for his grandparents' golden wedding. Madelief tags along. He and Madelief dislike the weird suit the shop assistants suggest to him, a feeling shared by the shop assistants themselves, who hate serving small children.

Hopping through the park, Madelief and Roos find a dead bird. This makes them think about death, and wonder if a motionless old man on a park bench is dead too. So they try to find out.

A mysterious aunt comes to visit Madelief and her mother. As the aunt is very strict, Madelief tries to behave, but gets irritated by her endless tales of illnesses.

Jan-Willem is grounded in his room by his mother for being disobedient. Yet Madelief is intent on visiting him, so, undeterred, she starts climbing the walls to his room on the first floor. Jan-Willem's mother catches her red-handed, but then Madelief thinks of using the phone to achieve her aim.

Roos meets a despondent man who has lost a leg, and tries to find himself a new one. Then Madelief and Jan-Willem turn up with a snail. They want to find out if salt will kill the snail, but Roos feels sorry and tries to rescue it.

Madelief and Roos meet a dubious, ineffective flower seller, who asks the girls to work for him. Going from door to door, the girls turn out to be far more successful than he, but is he willing to give them a fair share?

Roos and Jan-Willem are playing in the park, when they see a very sullen Madelief. It turns out that Madelief's mother has accepted a better paid job in the big city, which means they will have to move. Madelief feels bad about leaving her friends, and stubbornly refuses to go, so Jan-Willem wonders if he might hide her in his house.