You can't tell a soul
Our tale starts in the Shrieking Shack. Peter has managed to escape from his 'owner' and is enjoying peace and quiet in his human form while he can.
A poltergeist drifted through the tunnel from the Whomping Willow and shrieked. "The ghosts are quiet in here today!"
Peter jumped and gasped. "Who are you?"
The poltergeist bowed and smirked. "Peeves the poltergeist from Hogwarts School of Witchcraft and Wizardry. The real question is who are you?"
Peter muttered, "Peter Pettigrew."
Peeves smiled mischievously. "THERE'S A RUNAWAY IN THE SHRIEKING SHACK!"
Peter scowled. "You can't tell a soul."
Peeves said, "Now, why would a runaway care what a poltergeist does?"
Peter mumbled, "I'm not a runaway, I'm a criminal."
Peeves grinned. "A criminal, now I'm curious."
Peter frowned. "I don't want to talk about it."
Peeves replied, "Okay, I won't bring it up again. Why don't you come make some mischief with me? I can find you a hiding place."
Peter gasped. "You would really do that for a stranger?"
Peeves beamed, "You're not a stranger any more, you're a friend. Now, let's go!"