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.