Things could not have gone worse.

D'Aguilar had discovered the secret of his faith through his spies, and, having by some accursed mischance fallen in love with his daughter's beauty, was become his bitter enemy because he must refuse her to him.

Why must he refuse her?
The man was of great position and noble blood; she would become the wife of one of the first grandees of Spain, one who stood nearest to the throne.

Perhaps--such a thing was possible--she might live herself to be queen, or the mother of kings.

Moreover, that marriage meant safety for himself; it meant a quiet age, a peaceable death in his own bed--for, were he fifty times a Marano, who would touch the father-in-law of the Marquis de Morella?
Why?
Just because he had promised her in marriage to Peter Brome, and through all his life as a merchant he had never yet broken with a bargain because it went against himself.