He found it disconcerting that the faces and behaviour of his neighbours lacked anything he could grasp and secretly abuse.

They continued to converse with admirable and slightly conscious phlegm, yet he knew, as well as if each one had whispered to him privately, that this shady incident had shaken them.

Something unsettling to their notions of propriety-something dangerous and destructive of complacency--had occurred, and this was unforgivable.
Each had a different way, humorous or philosophic, contemptuous, sour, or sly, of showing this resentment.

But by a flash of insight Shelton saw that at the bottom of their minds and of his own the feeling was the same.

Because he shared in their resentment he was enraged with them and with himself.