On the way to the castle Sirius offers Harry the possibility to live with him, once he is absolved of all charges, which delights Harry immensely. Yet suddenly the clouds part and unveil the full moon. Professor Lupin changes into a werewolf and, as he has not taken his potion, he is dangerous, so Sirius changes into a dog and tries to protect the students from an attack. Peter uses the chaos to transform back into a rat and disappears.
Harry and Hermione follow Sirius′ yelp of pain and anguish and see hundreds of Dementors at the lake who threaten Sirius. With Hermione’s help Harry tries hard to conjure a Patronus, but fails miserably. When one of the Dementors prepares to kiss Harry he sees a white Patronus in the shape of a stag move over the lake towards him, dispelling all of the Dementors. Before he passes out he catches a glimpse of a person on the other side of the lake who looks very familiar.
