As the group leaves the Shrieking Shack and returns to the Whomping Willow, Black confesses that he is Harry’s godfather. He realizes that turning Pettigrew in will make him a free man, and he offers to let Harry stay with him instead of the Dursleys. Harry eagerly accepts, and Harry sees a smile in “Black’s gaunt face” (379) for the first time. However, the night is suddenly bathed in moonlight, and at the sight of the full moon, Hermione remembers that Lupin “didn’t take his potion tonight! He’s not safe!” (380).

As Lupin transforms into a werewolf, chaos breaks out. Peter Pettigrew breaks free, knocks Ron unconscious, and escapes into the night. Sirius tries to protect the others by transforming into a dog and fighting Lupin, but he is badly injured, and Lupin flees into the forest. Harry and Hermione find that Sirius has transformed back into a man, and there are over a hundred dementors closing in on him. Harry and Hermione try to use the Patronus Charm, but they aren’t strong enough, and the dementors close in on them, preparing to deliver the Dementor’s Kiss. Suddenly, “a silvery light [grows] brighter and brighter” (384), eventually driving the dementors away.