The Devil's Trap.

A small town is one day visited by a priest who is there on a secret mission. He is a member of the Inquisition sent to investigate the activities of a local miller. The miller and his son are the descendants of an old family whose ancestral home burned down a century ago, but was rebuilt from scratch. The miller inherited much of his knowledge about the land, water, and a building's stability from generations of family experience. His reputation for finding water and predicting when a structure might collapse have come to the attention of the Inquisition -surely he must be in league with the Devil.