A young sailor finds himself trapped in the labyrinthine mansion of his occultist uncle, along with a number of eccentric and mysterious relatives who all seem to be harboring a dark secret.
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.
