The Marauders' Reunion (PoA, Chap. 19)

To the tune of Gee, Officer Krupke

In the Shrieking Shack, SIRIUS and REMUS confront PETER after they force RON's rat to reveal itself.

REMUS:
Good evening, old friend, Peter,
It's so great to see you
Let's talk about some rumors
To find out if they're true
Did Harry Potter's parents
Get killed because of you?
If that's true, then we will kill you, too

PETER:
But how could I kill them if I didn't know
Where they were? Sirius betrayed them twelve years ago

SIRIUS:
And twelve years is how long
You've been by Ron's side
What a convenient way to hide!

PETER:
I was scared!
I was scared! I knew that
I'd be next in line
To be the victim of your next crime

REMUS:
Oh Peter, stop pretending
That you're the victim here
You were the Secret Keeper
To me that's crystal-clear
And then you went ahead and
You said to Voldemort-

PETER:
Please don't say the name of the Dark Lord!

SIRIUS:
What's wrong, are you scared to hear your master's name?
Well, after all, when he's in power, you'll be to blame
You'll die now the way they say you died that night

PETER:
But, Sirius, this isn't right! Listen, please
How could you escape from Azkaban without having Dark Powers close at hand?

SIRIUS:
I didn't need Dark powers
I had another plan
I turned right into Padfoot
And fled from Azkaban
I watched you hiding from me
You filthy, stinky rrrrrrrrrrat!

REMUS (to SIRIUS):
It's so great that you discovered that!

SIRIUS and REMUS:
You shouldn't have listened to your Voldemort

PETER:
But you two don't realize the power of the Dark Lord.
He threatened to kill me, so I had no choice

SIRIUS:
Peter, you always have a choice!
You should have died rather than betrayed your friends
But you didn't act in our defense

PETER (to SIRIUS):
Oh, Sirius I'm so sorry

SIRIUS:
Don't touch me, filthy rrrrrrrat.

PETER (to REMUS):
Oh, Remus, please forgive me.

REMUS:
Don't even think of that!

PETER (to RON):
But wasn't I a good pet? At least you can spare me!

RON:
You slept in my bed; get away from me!

REMUS and SIRIUS:
Well, Peter, old pal, it's been nice knowing you
But everything ends sometime and this friendship will, too
We won't spare your life now, so don't even try
Our hearts won't be softened
Goodbye!

HARRY (spoken): NO!

Sirius says "rrrrrat" because in the movie, Gary Oldman rolls his r's when he says to Peter, "You rrrrrat!" and when he says to Snape, "Rrrrrrremus and I have some unfinished business".