The family were seriously in danger of expulsion from Lone.
It was at this crisis that the devoted son came to the help of his father--not wisely, as many people thought then--not fortunately, as it turned out.

To prevent his father from being compelled to leave Lone, and to protect him from the persecution of creditors, the young Marquis of Arondelle performed an act of self-sacrifice and filial devotion seldom equalled in the world's history.

He renounced all his own entailed rights, and sold all his prospective life interest in Lone.

His was a young, strong life, good for fifty or sixty years longer.

His interest brought a sum large enough to pay off the mortgage on Lone and to settle all others of his father's outstanding debts.
Thus peaceable possession of Lone might have been secured to the family during the natural life of the duke.