Evidently all were expecting something and were filling up the interval with loud but irrelevant conversation.

When Stavrogin and Verhovensky appeared there was a sudden hush.
But I must be allowed to give a few explanations to make things clear.
I believe that all these people had come together in the agreeable expectation of hearing something particularly interesting, and had notice of it beforehand.

They were the flower of the reddest Radicalism of our ancient town, and had been carefully picked out by Virginsky for this "meeting." I may remark, too, that some of them (though not very many) had never visited him before.

Of course most of the guests had no clear idea why they had been summoned.

It was true that at that time all took Pyotr Stepanovitch for a fully authorised emissary from abroad; this idea had somehow taken root among them at once and naturally flattered them.