The Abbess of Vlaye by Stanley J. Weyman

Though it was not des Ageaux' fate to lie in one of those underground dungeons, noisome and dark, which the lords of an earlier century had provided in the foundations of the castle, he was not greatly the better for the immunity. The humiliations of the mind are sometimes sharper than the pains of the body; and the Lieutenant of Perigord, defeated and a prisoner, was little the happier though a dry strong-room looking on a tiny inner court held him, and though he suffered nothing from cold or the slimy companionship of the newt and frog. On the ambitious man defeat sits more heavily than chains; into the nature that would fain be at work inaction gnaws deeper than a shackle-bolt. Never while he lived would des Ageaux forget the long hours which he spent, gazing drearily on the blank wall that faced his window, while his mind measured a hundred times over the depth and the completeness of his fall.

He feared little for his life if he deigned to fear at all. He knew that he was a prize too valuable to be wasted. In the last resort, indeed, when all hopes had failed the Captain of Vlaye, and ruin stared him in the face, he might wreak his vengeance on the King's governor. But short of that moment -- and it depended upon many things -- the Lieutenant accounted himself safe. Safe as to life, but a beaten man, a prisoner, a failure; a blot, every moment he lay there, on the King's dignity, whose deputy he was; an unfortunate, whose ill hap would never be forgiven by the powers he had represented so ill.