It took a few seconds for the absurdity of this statement to sink in. Then Ron voiced what everyone was surely thinking.

'You're both mental.'

'Ridiculous!' said Hermione faintly

"How have you possibly come to that conclusion?" I said

'Peter Pettigrew's dead!' said Harry. 'He killed him twelve years ago!'

He pointed at Black, whose face twitched convulsively.

'I meant to,' he growled, his yellow teeth bared, 'but little Peter got the better of me … not this time, though!'

And Crookshanks was thrown to the floor as Black lunged at Scabbers; Ron yelled with pain as Black's weight fell on his broken leg. I started forwards, raising my wand, not about to let this madman get anywhere near my brother, but Lupin pushed me back and started dragging Black away from Ron himself.

'Sirius, NO!' Lupin yelled "'WAIT! You can't do it just like that – they need to understand – we've got to explain –'

'We can explain afterwards!' snarled Black, trying to throw Lupin off, one hand still clawing the air as it tried to reach Scabbers, who was squealing like a piglet, scratching Ron's face and neck as he tried to escape.

'They've – got – a – right – to – know – everything!' Lupin panted, still trying to restrain Black. 'Ron's kept him as a pet! There are parts of it even I don't understand! And Harry – you owe Harry the truth, Sirius!'

Black stopped struggling, though his hollowed eyes were still fixed on Scabbers, who was clamped tightly under Ron's bitten, scratched and bleeding hands.

'All right, then,' Black said, without taking his eyes off the rat. 'Tell them whatever you like. But make it quick, Remus. I want to commit the murder I was imprisoned for …'

'You're nutters, both of you,' said Ron shakily, looking round at Harry, Hermione and I for support. 'I've had enough of this. I'm off"

He tried to heave himself up on his good leg, but Lupin raised his wand again, pointing it at Scabbers.

'You're going to hear me out, Ron,' he said quietly. 'Just keep a tight hold on Peter while you listen.'

'HE'S NOT PETER, HE'S SCABBERS!' Ron yelled, trying to force the rat back into his front pocket, but Scabbers was fighting too hard; Ron swayed and overbalanced, and Harry caught him and pushed him back down to the bed. Then, ignoring Black, Harry turned to Lupin.

'There were witnesses who saw Pettigrew die,' he said. 'A whole street full of them …'

'They didn't see what they thought they saw!' said Black savagely, still watching Scabbers struggling in Ron's hands.

'Everyone thought Sirius killed Peter,' said Lupin, nodding. 'I believed it myself – until I saw the map tonight. Because the Marauder's Map never lies … Peter's alive. Ron's holding him, Harry"

This was reaching a new level of absurdity, how on earth could Scabbers be Peter Pettigrew? It made no sense whatsoever! They had both gone mad!

Then Hermione spoke, in a trembling, would-be calm sort of voice, as though trying to will Professor Lupin to talk sensibly.

'But Professor Lupin … Scabbers can't be Pettigrew … it just can't be true, you know it can't …'

'Why can't it be true?' Lupin said calmly, as though they were in class, and Hermione had simply spotted a problem in an experiment with Grindylows.

'Because … because people would know if Peter Pettigrew had been an Animagus. We did Animagi in class with Professor McGonagall. And I looked them up when I did my homework – the Ministry keeps tabs on witches and wizards who can become animals; there's a register showing what animal they become, and their markings and things … and I went and looked Professor McGonagall up on the register, and there have only been seven Animagi this century, and Pettigrew's name wasn't on the list –'

I laughed at this, the amount of effort Hermione put in to her homework was incredible.

'Right again, Hermione!' he said. 'But the Ministry never knew that there used to be three unregistered Animagi running around Hogwarts.'

'If you're going to tell them the story, get a move on, Remus,' snarled Black, who was still watching Scabbers's every desperate move. 'I've waited twelve years, I'm not going to wait much longer.'

'All right … but you'll need to help me, Sirius,' said Lupin, 'I only know how it began …'

Lupin proceeded to tell a long story about him becoming a werewolf, how Harry's father James, Black and Peter Pettigrew had all become Animagi to assist him during his transfigurations, how the Whomping Willow and the Shrieking Shack had been built for him, and how Black had played a joke on Snape which almost killed him. It consisted of telling Snape to go to the shack on the night of a full moon. If James hadn't gone after Snape, he would have been killed.

'So that's why Snape doesn't like you,' said Harry slowly, 'because he thought you were in on the joke?'

'That's right,' sneered a cold voice from the wall right behind me! I jumped and whipped around, to see Severus Snape pulling off the Invisibility Cloak, pointing his wand directly at Lupin!

Hermione screamed. Black leapt to his feet. Harry looked like he'd received a huge electric shock.

'I found this at the base of the Whomping Willow,' said Snape, throwing the Cloak aside, careful to keep his wand pointing directly at Lupin's chest. 'Very useful, Potter, I thank you …

I thought Harry would have to wash it very thoroughly later on after that greasy twat had his hands on it!

Snape was slightly breathless, but his face was full of suppressed triumph.

'You're wondering, perhaps, how I knew you were here?' he said, his eyes glittering. 'I've just been to your office, Lupin. You forgot to take your Potion tonight, so I took a gobletful along. And very lucky I did … lucky for me, I mean. Lying on your desk was a certain map. One glance at it told me all I needed to know. I saw you running along this passageway and out of sight.'

'Severus –' Lupin began, but Snape overrode him. 'I've told the Headmaster again and again that you've been helping your old friend Black into the castle, Lupin, and here's the proof. Not even I dreamed you would have the nerve to use this old place as your hideout –'

'Severus, you're making a mistake,' said Lupin urgently. 'You haven't heard everything – I can explain – Sirius is not here to kill Harry –'

'Two more for Azkaban tonight,' said Snape, his eyes now gleaming fanatically. 'I shall be interested to see how Dumbledore takes this … he was quite convinced you were harmless, you know, Lupin … a tame werewolf …'

'You fool,' said Lupin softly. 'Is a schoolboy grudge worth putting an innocent man back inside Azkaban?' BANG! Thin, snake-like cords burst from the end of Snape's wand and twisted themselves around Lupin's mouth, wrists and ankles; he over-balanced and fell to the floor, unable to move.

Clearly the answer to Lupin's question was a resounding yes! I started forwards.

"Professor, are you crazy?! If it turns out they're innocent, as unlikely as that sounds, you'll live to regret this! Surely we should listen to them first?!"

'Miss Weasley, you are already facing suspension from this school,' Snape spat. 'You, Potter, Granger and your brother are out of bounds, in the company of a convicted murderer and a werewolf. For once in your life, hold your tongue.'

'But if – if there was a mistake –'

'KEEP QUIET, YOU STUPID GIRL!' Snape shouted, looking suddenly quite deranged. 'DON'T TALK ABOUT WHAT YOU DON'T UNDERSTAND!

He then pointed his wand at Black.

'Vengeance is very sweet,' Snape breathed at Black. 'How I hoped I would be the one to catch you …'

'The joke's on you again, Severus,' snarled Black. 'As long as this boy brings his rat up to the castle –' he jerked his head at Ron, '– I'll come quietly …'

'Up to the castle?' said Snape silkily. 'I don't think we need to go that far. All I have to do is call the Dementors once we get out of the Willow. They'll be very pleased to see you, Black … pleased enough to give you a little kiss, I daresay …'

What little colour there was in Black's face left it. 'You – you've got to hear me out,' he croaked. 'The rat – look at the rat –'

This was enough for me! There was no way he was going to subject a potentially innocent man to the Dementors Kiss! I raised my wand, pointed it at Snape, and yelled "Expelliarmus!"

I wasn't the only one however. Harry, Ron and Hermione had also done the same. Snape was lifted off his feet. He smashed into the wall, the back of his head making a loud crack as it made contact, and he fell to the floor, unconscious.