“[…] for which [Thierry Tidrow] wrote an avant-garde score abundant with the joy of music-making and with a deep understanding of illustrative sounds, drawn from a wide range of playing and singing techniques that are popular in contemporary art music. Here is yet another inspired example that contemporary sounds, be they experimental, are outstandingly effective when well-tied to an exciting story for even the smallest of children.”

Bertil is a lonely child : his parents have to work every day and he has no one to play with. Then one day he meets Nils Karlsson, a little boy no bigger than a thumb! Nils lives in a mouse hole, and shares his secret with Bertil. This imaginative children's opera after Astrid Lindgren's classic children's book explores the power of friendship and imagination and integrates music and theatre in a novel way, with just a soprano and speaking violinist that put on the whole show.

The original mobile theatre production has toured kindergartens and children’s hospitals around Düsseldorf, Bonn, Dortmund, and later taken up by Oper Wupptertal and the Elbphilharmonie. A new production will be presented at Semperoper Dresden in 2021.