Harry, who was still playing the flute, waved at Ron to get his attention and pointed at himself.

'You want to go first? Are you sure?' said Ron. 'I don't know how deep this thing goes. Give the flute to Hermione so she can keep him asleep.'

Harry handed the flute over. In the few seconds' silence, the dog growled and twitched, but the moment Hermione began to play, it fell back into its deep sleep.

Harry climbed over it and looked down through the trapdoor. There was no sign of the bottom.

He lowered himself through the hole until he was hanging on by his fingertips. Then he looked up at Ron and said, 'If anything happens to me, don't follow. Go straight to the owlery and send Hedwig to Dumbledore, right?'

'Right,' said Ron.

'See you in a minute, I hope ...'

And Harry let go. Cold, damp air rushed past him as he fell down, down, down and FLUMP. With a funny, muffled sort of thump he landed on something soft. He sat up and felt around, his eyes not used to the gloom. It felt as though he was sitting on some sort of plant.

'It's OK!' he called up to the light the size of a postage stamp which was the open trapdoor. 'It's a soft landing, you can jump!'

Ron followed straight away. He landed sprawled next to Harry.

'What's this stuff?' were his first words.

'Dunno, sort of plant thing. I suppose it's here to break the fall. Come on, Hermione!'

The distant music stopped. There was a loud bark from the dog, but Hermione had already jumped. She landed on Harry's other side.

'We must be miles under the school,' she said.

'Lucky this plant thing's here, really,' said Ron.

'Lucky!' shrieked Hermione. 'Look at you both!'

She leapt up and struggled towards a damp wall. She had to struggle because the moment she had landed, the plant had started to twist snake-like tendrils around her ankles. As for Harry and Ron, their legs had already been bound tightly in long creepers without their noticing.

Hermione had managed to free herself before the plant got a firm grip on her. Now she watched in horror as the two boys fought to pull the plant off them, but the more they strained against it, the tighter and faster the plant wound around them.

'Stop moving!' Hermione ordered them. 'I know what this is it's Devil's Snare!'

'Oh, I'm so glad we know what it's called, that's a great help,' snarled Ron, leaning back, trying to stop the plant curling around his neck.

'Shut up, I'm trying to remember how to kill it!' said Hermione.

'Well, hurry up, I can't breathe!' Harry gasped, wrestling with it as it curled around his chest.

'Devil's Snare, Devil's Snare ... What did Professor Sprout say? It likes the dark and the damp '

'So light a fire!' Harry choked.

'Yes of course but there's no wood!' Hermione cried, wringing her hands.

'HAVE YOU GONE MAD?' Ron bellowed. 'ARE YOU A WITCH OR NOT?'

'Oh, right!' said Hermione, and she whipped out her wand, waved it, muttered something and sent a jet of the same bluebell flames she had used on Snape at the plant. In a matter of seconds, the two boys felt it loosening its grip as it cringed away from the light and warmth. Wriggling and flailing, it unravelled itself from their bodies and they were able to pull free.

'Lucky you pay attention in Herbology, Hermione,' said Harry as he joined her by the wall, wiping sweat off his face.

'Yeah,' said Ron, 'and lucky Harry doesn't lose his head in a crisis "there's no wood", honestly.'

'This way,' said Harry, pointing down a stone passageway which was the only way on.

All they could hear apart from their footsteps was the gentle drip of water trickling down the walls. The passageway sloped downwards and Harry was reminded of Gringotts. With an unpleasant jolt of the heart, he remembered the dragons said to be guarding vaults in the wizards' bank. If they met a dragon, a fully grown dragon Norbert had been bad enough ...

'Can you hear something?' Ron whispered.

Harry listened. A soft rustling and clinking seemed to be coming from up ahead.

'Do you think it's a ghost?'

'I don't know ... sounds like wings to me.'

'There's light ahead I can see something moving.'

They reached the end of the passageway and saw before them a brilliantly lit chamber, its ceiling arching high above them. It was full of small, jewel-bright birds, fluttering and tumbling all around the room. On the opposite side of the chamber was a heavy, wooden door.

'Do you think they'll attack us if we cross the room?' said Ron.

'Probably,' said Harry. 'They don't look very vicious, but I suppose if they all swooped down at once ... Well, there's nothing for it ... I'll run.'

He took a deep breath, covered his face with his arms and sprinted across the room. He expected to feel sharp beaks and claws tearing at him any second, but nothing happened. He reached the door untouched. He pulled the handle, but it was locked.

The other two followed him. They tugged and heaved at the door, but it wouldn't budge, not even when Hermione tried her Alohomora Charm.

'Now what?' said Ron.

'These birds ... they can't be here just for decoration,' said Hermione.

They watched the birds soaring overhead, glittering glittering?

'They're not birds!' Harry said suddenly, 'they're keys! Winged keys look carefully. So that must mean ...' he looked around the chamber while the other two squinted up at the flock of keys. '... Yes look! Broomsticks! We've got to catch the key to the door!'

'But there are hundreds of them!'

Ron examined the lock on the door.

'We're looking for a big, old-fashioned one probably silver, like the handle.'

They seized a broomstick each and kicked off into the air, soaring into the midst of the cloud of keys. They grabbed and snatched but the bewitched keys darted and dived so quickly it was almost impossible to catch one.

Not for nothing, though, was Harry the youngest Seeker in a century. He had a knack for spotting things other people didn't. After a minute's weaving about through the whirl of rainbow feathers, he noticed a large silver key that had a bent wing, as if it had already been caught and stuffed roughly into the keyhole.

'That one!' he called to the others. 'That big one there no, there with bright blue wings the feathers are all crumpled on one side.'

Ron went speeding in the direction that Harry was pointing, crashed into the ceiling and nearly fell off his broom.

'We've got to close in on it!' Harry called, not taking his eyes off the key with the damaged wing. 'Ron, you come at it from above Hermione, stay below and stop it going down and I'll try and catch it. Right, NOW!'

Ron dived, Hermione rocketed upwards, the key dodged them both and Harry streaked after it; it sped towards the wall, Harry leant forward and with a nasty crunching noise, pinned it against the stone with one hand. Ron and Hermione's cheers echoed around the high chamber.

They landed quickly and Harry ran to the door, the key struggling in his hand. He rammed it into the lock and turned it worked. The moment the lock had clicked open, the key took flight again, looking very battered now that it had been caught twice.

'Ready?' Harry asked the other two, his hand on the door handle. They nodded. He pulled the door open.

The next chamber was so dark they couldn't see anything at all. But as they stepped into it, light suddenly flooded the room to reveal an astonishing sight.

They were standing on the edge of a huge chessboard, behind the black chessmen, which were all taller than they were and carved from what looked like black stone. Facing them, way across the chamber, were the white pieces. Harry, Ron and Hermione shivered slightly the towering white chessmen had no faces.

'Now what do we do?' Harry whispered.

'It's obvious, isn't it?' said Ron. 'We've got to play our way across the room.'

Behind the white pieces they could see another door.

'How?' said Hermione nervously.

'I think,' said Ron, 'we're going to have to be chessmen.'

He walked up to a black knight and put his hand out to touch the knight's horse. At once, the stone sprang to life. The horse pawed the ground and the knight turned his helmeted head to look down at Ron.

'Do we er have to join you to get across?'

The black knight nodded. Ron turned to the other two.

'This wants thinking about ...' he said. 'I suppose we've got to take the place of three of the black pieces ...'

Harry and Hermione stayed quiet, watching Ron think. Finally he said, 'Now, don't be offended or anything, but neither of you are that good at chess '

'We're not offended,' said Harry quickly. 'Just tell us what to do.'

'Well, Harry, you take the place of that bishop, and Hermione, you go there instead of that castle.'

'What about you?'

'I'm going to be a knight,' said Ron.

The chessmen seemed to have been listening, because at these words a knight, a bishop and a castle turned their backs on the white pieces and walked off the board leaving three empty squares which Harry, Ron and Hermione took.

'White always plays first in chess,' said Ron, peering across the board. 'Yes ... look ...'

A white pawn had moved forward two squares.

Ron started to direct the black pieces. They moved silently wherever he sent them. Harry's knees were trembling. What if they lost?

'Harry move diagonally four squares to the right.'

Their first real shock came when their other knight was taken. The white queen smashed him to the floor and dragged him off the board, where he lay quite still, face down.

'Had to let that happen,' said Ron, looking shaken. 'Leaves you free to take that bishop, Hermione, go on.'

Every time one of their men was lost, the white pieces showed no mercy. Soon there was a huddle of limp black players slumped along the wall. Twice, Ron only just noticed in time that Harry and Hermione were in danger. He himself darted around the board taking almost as many white pieces as they had lost black ones.

'We're nearly there,' he muttered suddenly. 'Let me think let me think ...'

The white queen turned her blank face towards him.

'Yes ...' said Ron softly, 'it's the only way ... I've got to be taken.'

'NO!' Harry and Hermione shouted.

'That's chess!' snapped Ron. 'You've got to make some sacrifices! I'll make my move and she'll take me that leaves you free to checkmate the king, Harry!'

'But '

'Do you want to stop Snape or not?'

'Ron '

'Look, if you don't hurry up, he'll already have the Stone!'

There was nothing else for it.

'Ready?' Ron called, his face pale but determined. 'Here I go now, don't hang around once you've won.'

He stepped forward and the white queen pounced. She struck Ron hard around the head with her stone arm and he crashed to the floor Hermione screamed but stayed on her square the white queen dragged Ron to one side. He looked as if he'd been knocked out.

Shaking, Harry moved three spaces to the left.

The white king took off his crown and threw it at Harry's feet. They had won. The chessmen parted and bowed, leaving the door ahead clear. With one last desperate look back at Ron, Harry and Hermione charged through the door and up the next passageway.

'What if he's ?'

'He'll be all right,' said Harry, trying to convince himself. 'What do you reckon's next?'

'We've had Sprout's, that was the Devil's Snare Flitwick must've put charms on the keys McGonagall transfigured the chessmen to make them alive that leaves Quirrell's spell, and Snape's ...'

They had reached another door.

'All right?' Harry whispered.

'Go on.'