Malpertuis is the name of an old, rambling mansion which is in reality a labyrinth where characters from Greek mythology are imprisoned by the bedridden Cassavius. He manages to keep them, as well as his nephew and niece, prisoners even after his death, through a binding testament. As Jan, the nephew, unravels the mystery, he discovers that he cannot escape the house because Malpertuis is far more significant than he was led to believe.

Life in Gestapo jails in occupied Belgium.

A local brass band rehearses for a music competition in Bruges. They are confident that a new march by a young music teacher will get them the first prize. Their chance of winning seems to get an awful lot smaller when a a fight breaks out between the chairman and the music teacher -- urging the latter to sell the march to another band.