Two children, Cecilie and Fredrik, are sent by Dr. Krull to the planet Gyllenblå, where laughter and emotions have been banned by President Rasch. They meet Galaxia, a girl who helps them escape from the police and join the underground.
Cecilie and Fredrik about the history of Gyllenblå and the origin of the anti-laughter serum from Epicykel, a guerrilla member. They also discover that there is a hidden pyramid on the planet that holds the key to restoring laughter.
Cecilie and Fredrik are captured by the police and taken to a labyrinth where they are subjected to tests and interrogations by Rasch and his assistant Kubina. They escape with the help of Galaxia and Foton, another guerrilla member.
Cecilie and Fredrik reach the pyramid with Galaxia and Foton, but are pursued by Rasch and his robot army. They enter the pyramid and find a device that can control the stars. They use it to create a light show that makes everyone laugh.
Cecilie and Fredrik say goodbye to their friends on Gyllenblå and return to Earth with Dr. Krull. They bring back a sample of the anti-laughter serum for further research. They also realize that they have fallen in love with each other.