Karsten's mom comes home late from work one day, and she has a surprise… a kitten! Golden brown with a block spot around one eye – almost like a pirate! “What do you want to name him?” his big sister Siri asks. “Maybe Buster?” Mom recommends. “Or Messi?” says Dad. “The world's best football player!” “No,” Karsten says. “I want him to be called… LEO! That's a good name for a lion, and I hope he'll become best friends with Lion Cub.” When Karsten and Dad go to the library to borrow some books about cats, they forget to close the cage, and Leo is free to run about in the apartment. He swings from the ceiling lamps and has a fantastic time. Leo is a bit afraid of rabbits, and Ms. Rabbit doesn't like cats all that much, but she makes an exception since Leo will be living with Karsten. Karsten takes the role of cat-owner seriously, and in the end both children and stuffed animals become good friends with the kitten. The books about Karsten and Petra are among the most popular for children between 3 and 6. Themes focus primarily on friendship and playing. The first books about Karsten and Petra came out in 1992, and there are still new books about the two good friends coming out today. In recent years, many children have gotten to know Karsten, Petra and their stuffed animals through the films that have been made about them.
Tor Åge Bringsværd (1939–) has received many awards, as a writer and as a playwright. His works have been translated into 23 languages and his theatrical works have been staged in twelve countries. Bringsværd writes for all ages.