On a stage with both an orchestra and a theatre manager, a little play is unfolding. The play concerns the two tooth trolls, Karius and Baktus, who play havoc and lark about inside Jens's teeth.
As the curtain rises, we see Karius busy making a hole with a large drill. He's planning to drill an underground tunnel from his tooth over to Baktus's tooth. Karius is a pessimist, and reckons Jens will soon give up eating candies and snacks, while Baktus optimistically believes that Jens is none too fond of wholewheat bread and milk, so they can probably carry on having a high old time. So they carry on drilling and hammering and having a whale of a time.
In the distance, Jens is complaining because he's got such bad toothache. Then they hear Jens's mother telling him to brush his teeth. Karius gets scared and says to Baktus they should shout to Jens that he's not to do as his mother says.
Suddenly the toothbrush comes at them, so they dive into the nearest hole to hide. There's a lot of brushing and foaming outside, and when they eventually take a peek, they see that all the bits of food are gone and there's nothing left for them to eat. Then Jens's mouth opens wide again, and bright light is shone towards the tooth trolls. It's the dentist examining Jens's teeth! Karius and Baktus get scared and hide away. The dentist directs his drill and rinse water into Jens's mouth, and fills up all the holes, while Karius and Baktus fume over their nice home destroyed.
Now they have nowhere to hide, and when the toothbrush arrives with its great, polishing strokes, Karius and Baktus are carried off and rinsed out of Jens's mouth, down the plughole and out onto the open sea, where they sit on a raft, spying for new holes in somebody's teeth to crawl into.