Editing Severus Snape (section)

==== ''Harry Potter and the Prisoner of Azkaban'' ====
In ''[[Harry Potter and the Prisoner of Azkaban]]'', Snape demonstrates his expertise with potions by brewing the complex Wolfsbane potion for the new Defence Against the Dark Arts professor, [[Remus Lupin]].<ref name="Flight of the Fat Lady">{{HPref|book=3|chapter=8}}</ref> Throughout the third book, Snape suspects that Lupin may be helping Harry's godfather [[Sirius Black]] enter Hogwarts castle; Sirius had been convicted (wrongly, as it is later revealed) of murdering [[Peter Pettigrew (character)|Peter Pettigrew]] and innocent bystanders, and betraying the Potter family's hiding place to Voldemort. This suspicion stems from Lupin's friendship with Sirius and Harry's father, James, while they were all at Hogwarts as students.<ref name="Snape's Worst Memory">{{HPref|book=5|chapter=28}}</ref> Near the climax of the book, Snape attempts to apprehend Sirius, but Sirius escapes with Harry's aid. Snape informs Dumbledore of this circumstance, and when Harry and Lupin are not punished, Snape retaliates by revealing to the entire school that Lupin is a [[werewolf (Harry Potter)|werewolf]], forcing the latter to resign his post.<ref name="Owl Post Again">{{HPref|book=3|chapter=22}}</ref>

''Prisoner of Azkaban'' reveals more details about the connection between Snape and James. While in school together, Sirius once tricked Snape into almost entering the [[Shrieking Shack]] while Lupin was there, transformed into a werewolf. James realised the danger and stopped Snape, saving his life; this is the incident Dumbledore referred to at the end of the first book. Snape, however, believes James' actions were self-serving, to avoid being expelled.<ref name="Moony, Wormtail, Padfoot, and Prongs">{{HPref|book=3|chapter=18}}</ref>