Well, if Myshkin is going to be the guy, he needs to be trotted out in front of society, so society can vote him up or down. If this seems like a very sudden, last-minute subplot in this book—well, yeah, kinda, but, hey, all those stories about people on the verge of death weren't going to tell themselves, so this had to wait apparently.
Anyhoodle, the Epanchins are waiting with bated breath to see if their potential new son-in-law will pass muster in the eyes of their social circle, so they throw a small dinner party for some selected people, including Princess Belokonsky, who has a solid upper crust rep and can boost Myshkin's if need be (and if she likes him).
Everyone is freaking out that he is going to do something wackadoo in public, like he always does. Myshkin doesn't really get that there is some stress around this issue, but also he doesn't really get the importance of this party in general.
Aglaya tries to have a conversation with him about this, giving him helpful pointers like: don't fall down, don't break stuff, and don't talk. Myshkin stresses that he won't necessarily be able to avoid doing any of these, but promises to try to his best. (Incidentally, is it just us, or is it not really clear what particularly embarrassing things Myshkin does around other people? As far as we can tell, his main social faux pas is trying to have serious conversations with people about his deep thoughts, instead of just going with the light chitchat they are expecting. But here, it suddenly sounds like he's some kind of walking clown doofus. Huh.)
That night, Myshkin has feverish anxiety dreams.
When he wakes up, he gets a visit from a totally wasted Lebedev, who has just come from the Epanchin house.
Through some super-convoluted means he intercepted a letter that Aglaya had sent to Rogozhin, and the note she sent to Ganya (the one we saw earlier, to meet her at the bench). Lebedev is all psyched that he can show these to Myshkin, but Myshkin is horrified at the idea of intercepting correspondence.
He is a little disturbed by the Ganya thing, but does nothing about it. The letter and the note get passed along to their intended recipients.
That afternoon is the afternoon when General Ivolgin has his stroke. Myshkin goes over to that house (where Ippolit is no longer living, by the way), and tries to help.
Lebedev comes too, and is overwrought with sadness about the general, and seems to blame himself for what's happened to him. Which, yeah, duh, brainiac.
Finally, it's time for the party. Myshkin is at first nervous, and this makes him act perfectly. He is dressed well, acts with good manners, is quiet and reserved, but not weird.
For his part, he is totally charmed with all the people there. They seem to him to be so friendly, so close, so nice, so attentive, and so interesting, that he is awash in happy feelings.
What is he not really getting? That this are just drawing-room manners, that half the people there hate the other half, that their interesting stories are actually the same old tired anecdotes they keep pulling out at every one of these parties, and that basically, this is all the kind of pleasant nothingness that civilized people put on in social gatherings.
The more happy Myshkin is, the more he starts to feel the urge to start talking. Uh-oh.