PoA: Chapters 17 & 18

In today's episode Chapter 17: Cat, Rat & Dog and Chapter 18: Moony, Wormtail, Pradfoot & Prongs. We're in the final stretch of the Prisoner of Azkaban with Harry, Ron and Hermione finding their way inside of the Whomping Willow and meet Sirius Black for the first time. He's clearly lost his mind and wants to kill a.....rat? Lupin saves the day - or does he - as the professor the kids once trusted with their lives reveals some unsettling facts about himself and his friendships directly related to Harry.