In the first place, Giovanni might kill him.

Del Ferice was a very good fencer, but Saracinesca was stronger and more active; there was certainly considerable danger in the duel.

On the other hand, if he survived, Giovanni had him in his power for the rest of his life, and there was no escape possible.

He had been caught listening--caught in a flagrantly dishonest trick--and he well knew that if the matter had been brought before a jury of honour, he would have been declared incompetent to claim any satisfaction.
It was not the first time Del Ferice had done such things, but it was the first time he had been caught.

He cursed his awkwardness in oversetting the vase just at the moment when his game was successfully played to the end--just when he thought that he began to see land, in having discovered beyond all doubt that Giovanni was devoted body and soul to Corona d'Astrardente.