Myshkin tries to see General Epanchin, but he isn't at home.
Then he goes to meet up with Kolya, waits around for a while, but Kolya doesn't seem to be coming back to his hotel.
Myshkin then starts wandering around Petersburg, and we get a long chapter basically from inside his head.
There are three things going on in the sort of confused stream-of-consciousness:
(1) Myshkin feels like Rogozhin is following him around but tries to ignore this feeling of paranoia.
(2) Myshkin is half-panicky, half-longing to see Nastasya again, though he cannot ever imagine a sexual relationship with her.
(3) Myshkin is starting to get the warning symptoms that an epileptic fit is on its way. This is most notably a feeling of complete peace and a sense of a higher plane of existence. (This is actually what Dostoevsky himself used to describe feeling just before his own epileptic seizures.)
So, he wanders around, tries not think about Nastasya, but still somehow ends up at the house where she is staying.
The landlady tells him that she is not there.
As he walks away, Myshkin suddenly realizes how this will look to Rogozhin, who is clearly stalking him now. After all, Myshkin totally promised that he wasn't in Petersburg because of Nastasya and that he didn't want anything to do with her, and then the first place he goes is her house.
Myshkin goes back to his hotel where he sees a man hiding under a stairway. It's Rogozhin. He's got a knife. He goes to stab Myshkin, but Myshkin immediately has a seizure and falls down.
Rogozhin runs off, and after a few minutes, Kolya happens to come to the hotel looking for Myshkin and identifies the seizure for what it is.
Myshkin eventually comes to, goes to recuperate at Lebedev's house, and three days later, they go out to the country to the Pavlosk dachas.