Snape, who holds a childhood grudge against the Marauders, arrives to apprehend Black but is knocked unconscious by Harry, Ron, and Hermione. Lupin and Black transform Pettigrew into human form and prepare to kill him, but Harry stops them, and convinces them to send Pettigrew to Azkaban instead. While returning to Hogwarts, Lupin, who had forgotten the full moon, transforms into a werewolf and attacks them. Pettigrew escapes, and Harry, Hermione, and Black are set upon by Dementors. A Patronus cast by a mysterious figure rescues them.