Snape was standing there.

'Good afternoon,' he said smoothly.

They stared at him.

'You shouldn't be inside on a day like this,' he said, with an odd, twisted smile.

'We were ' Harry began, without any idea what he was going to say.

'You want to be more careful,' said Snape. 'Hanging around like this, people will think you're up to something. And Gryffindor really can't afford to lose any more points, can they?'

Harry flushed. They turned to go back outside, but Snape called them back.

'Be warned, Potter any more night-time wanderings and I will personally make sure you are expelled. Good day to you.'

He strode off in the direction of the staff room.

Out on the stone steps, Harry turned to the others.

'Right, here's what we've got to do,' he whispered urgently. 'One of us has got to keep an eye on Snape wait outside the staff room and follow him if he leaves it. Hermione, you'd better do that.'

'Why me?'

'It's obvious,' said Ron. 'You can pretend to be waiting for Professor Flitwick, you know.' He put on a high voice, 'Oh Professor Flitwick, I'm so worried, I think I got question fourteen b wrong ...'

'Oh, shut up,' said Hermione, but she agreed to go and watch out for Snape.

'And we'd better stay outside the third-floor corridor,' Harry told Ron. 'Come on.'

But that part of the plan didn't work. No sooner had they reached the door separating Fluffy from the rest of the school than Professor McGonagall turned up again, and this time, she lost her temper.

'I suppose you think you're harder to get past than a pack of enchantments!' she stormed. 'Enough of this nonsense! If I hear you've come anywhere near here again, I'll take another fifty points from Gryffindor! Yes, Weasley, from my own house!'

Harry and Ron went back to the common room. Harry had just said, 'At least Hermione's on Snape's tail,' when the portrait of the Fat Lady swung open and Hermione came in.

'I'm sorry, Harry!' she wailed. 'Snape came out and asked me what I was doing, so I said I was waiting for Flitwick, and Snape went to get him, and I've only just got away. I don't know where Snape went.'

'Well, that's it then, isn't it?' Harry said.

The other two stared at him. He was pale and his eyes were glittering.

'I'm going out of here tonight and I'm going to try and get to the Stone first.'

'You're mad!' said Ron.

'You can't!' said Hermione. 'After what McGonagall and Snape have said? You'll be expelled!'

'SO WHAT?' Harry shouted. 'Don't you understand? If Snape gets hold of the Stone, Voldemort's coming back! Haven't you heard what it was like when he was trying to take over? There won't be any Hogwarts to get expelled from! He'll flatten it, or turn it into a school for the Dark Arts! Losing points doesn't matter any more, can't you see? D'you think he'll leave you and your families alone if Gryffindor win the House Cup? If I get caught before I can get to the Stone, well, I'll have to go back to the Dursleys and wait for Voldemort to find me there. It's only dying a bit later than I would have done, because I'm never going over to the Dark Side! I'm going through that trapdoor tonight and nothing you two say is going to stop me! Voldemort killed my parents, remember?'

He glared at them.

'You're right, Harry,' said Hermione in a small voice.

'I'll use the Invisibility Cloak,' said Harry. 'It's just lucky I got it back.'

'But will it cover all three of us?' said Ron.

'All all three of us?'

'Oh, come off it, you don't think we'd let you go alone?'

'Of course not,' said Hermione briskly. 'How do you think you'd get to the Stone without us? I'd better go and look through my books, there might be something useful ...'

'But if we get caught, you two will be expelled, too.'

'Not if I can help it,' said Hermione grimly. 'Flitwick told me in secret that I got a hundred and twelve per cent on his exam. They're not throwing me out after that.'

After dinner the three of them sat nervously apart in the common room. Nobody bothered them; none of the Gryffindors had anything to say to Harry any more, after all. This was the first night he hadn't been upset by it. Hermione was skimming through all her notes, hoping to come across one of the enchantments they were about to try and break. Harry and Ron didn't talk much. Both of them were thinking about what they were about to do.

Slowly, the room emptied as people drifted off to bed.

'Better get the Cloak,' Ron muttered, as Lee Jordan finally left, stretching and yawning. Harry ran upstairs to their dark dormitory. He pulled out the Cloak and then his eyes fell on the flute Hagrid had given him for Christmas. He pocketed it to use on Fluffy he didn't feel much like singing.

He ran back down to the common room.

'We'd better put the Cloak on here, and make sure it covers all three of us if Filch spots one of our feet wandering along on its own '

'What are you doing?' said a voice from the corner of the room. Neville appeared from behind an armchair, clutching Trevor the toad, who looked as though he'd been making another bid for freedom.

'Nothing, Neville, nothing,' said Harry, hurriedly putting the Cloak behind his back.

Neville stared at their guilty faces.

'You're going out again,' he said.

'No, no, no,' said Hermione. 'No, we're not. Why don't you go to bed, Neville?'

Harry looked at the grandfather clock by the door. They couldn't afford to waste any more time, Snape might even now be playing Fluffy to sleep.

'You can't go out,' said Neville, 'you'll be caught again. Gryffindor will be in even more trouble.'

'You don't understand,' said Harry, 'this is important.'

But Neville was clearly steeling himself to do something desperate.

'I won't let you do it,' he said, hurrying to stand in front of the portrait hole. 'I'll I'll fight you!'

'Neville,' Ron exploded, 'get away from that hole and don't be an idiot '

'Don't you call me an idiot!' said Neville. 'I don't think you should be breaking any more rules! And you were the one who told me to stand up to people!'

'Yes, but not to us,' said Ron in exasperation. 'Neville, you don't know what you're doing.'

He took a step forward and Neville dropped Trevor the toad, who leapt out of sight.

'Go on then, try and hit me!' said Neville, raising his fists. 'I'm ready!'

Harry turned to Hermione.

'Do something,' he said desperately.

Hermione stepped forward.

'Neville,' she said, 'I'm really, really sorry about this.'

She raised her wand.

'Petrificus Totalus!' she cried, pointing it at Neville.

Neville's arms snapped to his sides. His legs sprang together. His whole body rigid, he swayed where he stood and then fell flat on his face, stiff as a board.

Hermione ran to turn him over. Neville's jaws were jammed together so he couldn't speak. Only his eyes were moving, looking at them in horror.

'What've you done to him?' Harry whispered.

'It's the full Body-Bind,' said Hermione miserably. 'Oh, Neville, I'm so sorry.'

'We had to, Neville, no time to explain,' said Harry.

'You'll understand later, Neville,' said Ron, as they stepped over him and pulled on the Invisibility Cloak.

But leaving Neville lying motionless on the floor didn't feel like a very good omen. In their nervous state, every statue's shadow looked like Filch, every distant breath of wind sounded like Peeves swooping down on them.

At the foot of the first set of stairs, they spotted Mrs Norris skulking near the top.

'Oh, let's kick her, just this once,' Ron whispered in Harry's ear, but Harry shook his head. As they climbed carefully around her, Mrs Norris turned her lamp-like eyes on them, but didn't do anything.

They didn't meet anyone else until they reached the staircase up to the third floor. Peeves was bobbing halfway up, loosening the carpet so that people would trip.

'Who's there?' he said suddenly as they climbed towards him. He narrowed his wicked black eyes. 'Know you're there, even if I can't see you. Are you ghoulie or ghostie or wee student beastie?'

He rose up in the air and floated there, squinting at them.

'Should call Filch, I should, if something's a-creeping around unseen.'

Harry had a sudden idea.

'Peeves,' he said, in a hoarse whisper, 'the Bloody Baron has his own reasons for being invisible.'

Peeves almost fell out of the air in shock. He caught himself in time and hovered about a foot off the stairs.

'So sorry, your bloodiness, Mr Baron, sir,' he said greasily. 'My mistake, my mistake I didn't see you of course I didn't, you're invisible forgive old Peevsie his little joke, sir.'

'I have business here, Peeves,' croaked Harry. 'Stay away from this place tonight.'

'I will, sir, I most certainly will,' said Peeves, rising up in the air again. 'Hope your business goes well, Baron, I'll not bother you.'

And he scooted off.

'Brilliant, Harry!' whispered Ron.

A few seconds later, they were there, outside the third-floor corridor and the door was already ajar.

'Well, there you are,' Harry said quietly. 'Snape's already got past Fluffy.'

Seeing the open door somehow seemed to impress upon all three of them what was facing them. Underneath the Cloak, Harry turned to the other two.

'If you want to go back, I won't blame you,' he said. 'You can take the Cloak, I won't need it now.'

'Don't be stupid,' said Ron.

'We're coming,' said Hermione.

Harry pushed the door open.

As the door creaked, low, rumbling growls met their ears. All three of the dog's noses sniffed madly in their direction, even though it couldn't see them.

'What's that at its feet?' Hermione whispered.

'Looks like a harp,' said Ron. 'Snape must have left it there.'

'It must wake up the moment you stop playing,' said Harry. 'Well, here goes ...'

He put Hagrid's flute to his lips and blew. It wasn't really a tune, but from the first note the beast's eyes began to droop. Harry hardly drew breath. Slowly, the dog's growls ceased it tottered on its paws and fell to its knees, then it slumped to the ground, fast asleep.

'Keep playing,' Ron warned Harry as they slipped out of the Cloak and crept towards the trapdoor. They could feel the dog's hot, smelly breath as they approached the giant heads.

'I think we'll be able to pull the door open,' said Ron, peering over the dog's back. 'Want to go first, Hermione?'

'No, I don't!'

'All right.' Ron gritted his teeth and stepped carefully over the dog's legs. He bent and pulled the ring of the trapdoor, which swung up and open.

'What can you see?' Hermione said anxiously.

'Nothing just black there's no way of climbing down, we'll just have to drop.'