Baron Trigault's Vengeance by Emile Gaboriau

The old legend of Achilles's heel will be eternally true. A man may be humble or powerful, feeble or strong, but there are none of us without some weak spot in our armor, a spot vulnerable beyond all others, a certain place where wounds prove most dangerous and painful. M. Isidore Fortunat's weak place was his cash-box. To attack him there was to endanger his life -- to wound him at a point where all his sensibility centred. For it was in this cash-box and not in his breast that his heart really throbbed. His safe made him happy or dejected. Happy when it was filled to overflowing by some brilliant operation, and dejected when he saw it become empty as some imprudent transaction failed.

This then explains his frenzy on that ill-fated Sunday, when, after being brutally dismissed by M. Wilkie, he returned to his rooms in the company of his clerk, Victor Chupin. This explains, too, the intensity of the hatred he now felt for the Marquis de Valorsay and the Viscount de Coralth. The former, the marquis, had defrauded him of forty thousand francs in glittering gold. The other, the viscount, had suddenly sprung up out of the ground, and carried off from under his very nose that magnificent prize, the Chalusse inheritance, which he had considered as good as won. And he had not only been defrauded and swindled -- such were his own expressions -- but he had been tricked, deceived, duped, and outwitted, and by whom? By people who did not make it their profession to be shrewd, like he did himself. Just fancy, his business was to outwit others, and a couple of mere amateurs had outgeneraled him.