Just got into the first really really long party of the book. It happens so innocuously. The narrator just goes to visit his old friend Mme Villeparisis. And then he sees one person. And describes them. And another person. And talks to them. And before you know it a hundred pages have gone by.
In this case the party comes after he meets his friend Robert's mistress and goes to see her in a play. So we've actually spent several hundred pages on a single evening.