Sirius Black: The Death Eaters at the World Cup, your name rising from that goblet... these are not just coincidences. Hogwarts isn't safe anymore.
Harry Potter: What are you saying?
Sirius Black: I'm saying the devils are inside the walls. Igor Karkaroff? He was a Death Eater. And no one, no one stops being a Death Eater. Then there's Barty Crouch. Heart of stone. Sent his own son to Azkaban.
Harry Potter: You think one of them put my name in the goblet?
Sirius Black: I haven't a clue who put your name in that goblet... but whoever did is no friend to you. People die in this tournament.
(Sirius saying goodbye to Harry and Hermione...)
Sirius Black (to Harry): It's cruel that I spent so much time with James and Lily, and you so little. But know this: The ones that love us never really leave us. And you can always find them... in here. (to Hermione): You really are the brightest witch of your age.
Sirius Black: Sorry about the bite. I reckon that twinges a bit.
Ron Weasley: A bit? A bit? You almost tore my leg off!
Sirius Black: I was going for the rat. Normally, I have a very sweet disposition as a dog. In fact, more than once, James suggested that I make the change permanent. The tail I could live with. But the fleas, they're murder.
Severus Snape: I told Dumbledore you were helping an old friend into the castle. And now, here's the proof.
Sirius Black: Brilliant, Snape. You've put your keen mind to the task and come to the wrong conclusion. Now, if you'll excuse us, Remus and I have some unfinished business to attend to.
(Snape puts his wand at Sirius' throat...)
Severus Snape: Give me a reason. I beg you!
Remus Lupin: Severus, don't be a fool.
Sirius Black: He can't help it. It's habit by now.
Remus Lupin: Be quiet.
Sirius Black: Be quiet yourself, Remus!
Severus Snape: You two, quarrelling like an old married couple.
Sirius Black: Enough talk, Remus! Come on, let's kill him!
Remus Lupin: Wait!
Sirius Black: I did my waiting! Twelve years of it! In Azkaban!
Remus Lupin: Very well. Kill him. But wait one more minute. Harry has the right to know why.
Harry Potter: I know why. You betrayed my parents. You're the reason they're dead!
Remus Lupin: No, Harry, it wasn't him. Somebody did betray your parents... but it was somebody who, until quite recently, I believed to be dead!