In my e-book copy it happens on page 331, 332, and 333 out of 786. Arya recently tried to tell Ned about Varys and Illyro but she never saw their faces and it sounds like a fantasy to Ned thus he discounts her story about someone trying to kill him. Yoren shows up and meets Arya thinking she is a boy at first, he tells Ned that he has riden here as fast as possible for Ned deserves to hear the news from friendly ears and not sellswords. Yoren then asks to be alone and thus Arya is escorted out via Desmond. We are never privy to what Yoren talked to Ned about for Arya leaves the room and it is her pov, but it is quite obvious that it is about Catelyn kidnapping Tyrion.