On the day of Buckbeaks execution, the trio went down to talk to Hagrid before it happened. They rushed out of Hagrids house as it was time and the minister was coming.
As they ran Scabbers ran away so Ron went after him. Then a black dog came and bit Rons leg and took him.
Hermion and Harry fought the WIllow and and went through the tunnel. They saw Ron laying on the bed with a squirming Scabbers. Harry asked him where the dog went, but Ron replied saying thta Sirius Black was the dog and was an Animagus. Harry tried to fight Sirius. The Lupin came and disarmed them and hugged Sirius! HErmione shouted ta him saying he was a werewolf! Soon they caught Peter and revealed the ruth! Scabbers was Peter and he betrayed the Potters. Snape appeared and almost ruined the day. As they all exited happily, Lupin turned into a werewolf and Peter escaped. Sirius and Harry almost had their souls sucked out!