Peter Pettigrew's Exposure and Flight
Harry Potter and the Prisoner of AzkabanThe unmasking of Peter Pettigrew as the true traitor, his transformation back to human, and his escape to rejoin Voldemort.
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Bearing strength in each event
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Pettigrew as Scabbers

The Rat
The Disguise
Peter Pettigrew faked his death by cutting off his finger and transforming into a rat. He lived as Scabbers, first with the Weasley family, then with Ron at Hogwarts. He remained hidden for twelve years, listening to news and waiting for the Dark Lord's return.
The Telltale Signs
Scabbers is old, balding, and missing a toe. He is nervous around Crookshanks, who recognizes him as an Animagus. He tries to escape whenever Sirius is near. Ron attributes his behavior to illness, but the signs are there.
The Discovery
When Sirius escapes, Pettigrew becomes desperate. He attempts to flee, but is caught in the Shrieking Shack. Forced to transform back, he stands exposed as a balding, rat-like man. He tries to beg for mercy, but his cowardice is evident.
Pettigrew's confession and escape

The Traitor's Tale
The Confession
Pettigrew admits he was the spy for Voldemort. He was James and Lily's Secret-Keeper and betrayed them. He also killed twelve Muggles to fake his death. He pleads for his life, saying he was afraid of Voldemort.
The Mercy
Harry stops Sirius and Lupin from killing him, arguing that his father wouldn't want them to become murderers. Pettigrew is tied up and about to be taken to the castle, but the full moon causes Lupin to transform into a werewolf. In the chaos, Pettigrew grabs a wand, stuns Ron, and transforms back into a rat, escaping into the night.
The Aftermath
Pettigrew's escape is a major setback. He is now free to rejoin Voldemort. Harry is worried that he will help the Dark Lord rise again. Dumbledore reassures Harry that Pettigrew owes him a life debt, which may one day prove useful.
Twelve years as a rat, ending at Hogwarts
During the Shrieking Shack confrontation