ferocity

The son, on the other hand, had dropped all that jaunty, dashing style which had characterized him, and the ferocity of a dangerous wild beast gleamed in his dark eyes and distorted his handsome features.

I remembered the case well, for it was one in which Holmes had taken an interest on account of the peculiar ferocity of the crime and the wanton brutality which had marked all the actions of the assassin.