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.
Each year Thomas goes an a pilgrimage but he has more difficulty to complete it, but then he is offered a footbath that appears to contain a miracle drug. Wouldn't this make a huge seller during Expo 58 in Brussels... .
A strange man arrives in Belder on horseback, and introduces himself as Captain Zeppos. Initially, he is met with suspicion and jealousy, but he soon befriends a local, Ben Kurrel. It becomes apparent that Zeppos had a motive to come to Belder: when in Greece a stranger had made him an offer on a piece of land he had inherited near the town. Ben Kurrel and his friend Rita Mees help him investigate the mystery.
