Neville clutched the sleeve of Harry's robe and made a choking noise.

'That's your lookout, isn't it?' said Filch, his voice cracking with glee. 'Should've thought of them werewolves before you got in trouble, shouldn't you?'

Hagrid came striding towards them out of the dark, Fang at his heel. He was carrying his large crossbow, and a quiver of arrows hung over his shoulder.

'Abou' time,' he said. 'I bin waitin' fer half an hour already. All right, Harry, Hermione?'

'I shouldn't be too friendly to them, Hagrid,' said Filch coldly, 'they're here to be punished, after all.'

'That's why yer late, is it?' said Hagrid, frowning at Filch. 'Bin lecturin' them, eh? 'Snot your place ter do that. Yeh've done yer bit, I'll take over from here.'

'I'll be back at dawn,' said Filch, 'for what's left of them,' he added nastily, and he turned and started back towards the castle, his lamp bobbing away in the darkness.

Malfoy now turned to Hagrid.

'I'm not going in that Forest,' he said, and Harry was pleased to hear the note of panic in his voice.

'Yeh are if yeh want ter stay at Hogwarts,' said Hagrid fiercely. 'Yeh've done wrong an' now yeh've got ter pay fer it.'

'But this is servant stuff, it's not for students to do. I thought we'd be writing lines or something. If my father knew I was doing this, he'd '

' tell yer that's how it is at Hogwarts,' Hagrid growled. 'Writin' lines! What good's that ter anyone? Yeh'll do summat useful or yeh'll get out. If yeh think yer father'd rather you were expelled, then get back off ter the castle an' pack. Go on!'

Malfoy didn't move. He looked at Hagrid furiously but then dropped his gaze.

'Right then,' said Hagrid, 'now, listen carefully, 'cause it's dangerous what we're gonna do tonight an' I don' want no one takin' risks. Follow me over here a moment.'

He led them to the very edge of the Forest. Holding his lamp up high he pointed down a narrow, winding earth track that disappeared into the thick black trees. A light breeze lifted their hair as they looked into the Forest.

'Look there,' said Hagrid, 'see that stuff shinin' on the ground? Silvery stuff? That's unicorn blood. There's a unicorn in there bin hurt badly by summat. This is the second time in a week. I found one dead last Wednesday. We're gonna try an' find the poor thing. We might have ter put it out of its misery.'

'And what if whatever hurt the unicorn finds us first?' said Malfoy, unable to keep the fear out of his voice.

'There's nothin' that lives in the Forest that'll hurt yeh if yer with me or Fang,' said Hagrid. 'An' keep ter the path. Right, now, we're gonna split inter two parties an' follow the trail in diff'rent directions. There's blood all over the place, it must've bin staggerin' around since last night at least.'

'I want Fang,' said Malfoy quickly, looking at Fang's long teeth.

'All right, but I warn yeh, he's a coward,' said Hagrid. 'So me, Harry an' Hermione'll go one way an' Draco, Neville an' Fang'll go the other. Now, if any of us finds the unicorn, we'll send up green sparks, right? Get yer wands out an' practise now that's it an' if anyone gets in trouble, send up red sparks, an' we'll all come an' find yeh so, be careful let's go.'

The Forest was black and silent. A little way into it they reached a fork in the earth path and Harry, Hermione and Hagrid took the left path while Malfoy, Neville and Fang took the right.

They walked in silence, their eyes on the ground. Every now and then a ray of moonlight through the branches above lit a spot of silver blue blood on the fallen leaves.

Harry saw that Hagrid looked very worried.

'Could a werewolf be killing the unicorns?' Harry asked.

'Not fast enough,' said Hagrid. 'It's not easy ter catch a unicorn, they're powerful magic creatures. I never knew one ter be hurt before.'

They walked past a mossy tree-stump. Harry could hear running water; there must be a stream somewhere close by. There were still spots of unicorn blood here and there along the winding path.

'You all right, Hermione?' Hagrid whispered. 'Don' worry, it can't've gone far if it's this badly hurt an' then we'll be able ter GET BEHIND THAT TREE!'

Hagrid seized Harry and Hermione and hoisted them off the path behind a towering oak. He pulled out an arrow and fitted it into his crossbow, raising it, ready to fire. The three of them listened. Something was slithering over dead leaves nearby: it sounded like a cloak trailing along the ground. Hagrid was squinting up the dark path, but after a few seconds, the sound faded away.

'I knew it,' he murmured. 'There's summat in here that shouldn' be.'

'A werewolf?' Harry suggested.

'That wasn' no werewolf an' it wasn' no unicorn, neither,' said Hagrid grimly. 'Right, follow me, but careful, now.'

They walked more slowly, ears straining for the faintest sound. Suddenly, in a clearing ahead, something definitely moved.

'Who's there?' Hagrid called. 'Show yerself I'm armed!'

And into the clearing came was it a man, or a horse? To the waist, a man, with red hair and beard, but below that was a horse's gleaming chestnut body with a long, reddish tail. Harry and Hermione's jaws dropped.

'Oh, it's you, Ronan,' said Hagrid in relief. 'How are yeh?'

He walked forward and shook the centaur's hand.

'Good evening to you, Hagrid,' said Ronan. He had a deep, sorrowful voice. 'Were you going to shoot me?'

'Can't be too careful, Ronan,' said Hagrid, patting his crossbow. 'There's summat bad loose in this Forest. This is Harry Potter an' Hermione Granger, by the way. Students up at the school. An' this is Ronan, you two. He's a centaur.'

'We'd noticed,' said Hermione faintly.

'Good evening,' said Ronan. 'Students, are you? And do you learn much, up at the school?'

'Erm '

'A bit,' said Hermione timidly.

'A bit. Well, that's something.' Ronan sighed. He flung back his head and stared at the sky. 'Mars is bright tonight.'

'Yeah,' said Hagrid, glancing up too. 'Listen, I'm glad we've run inter yeh, Ronan, 'cause there's a unicorn bin hurt you seen anythin'?'

Ronan didn't answer immediately. He stared unblinkingly upwards, then sighed again.

'Always the innocent are the first victims,' he said. 'So it has been for ages past, so it is now.'

'Yeah,' said Hagrid, 'but have yeh seen anythin', Ronan? Anythin' unusual?'

'Mars is bright tonight,' Ronan repeated while Hagrid watched him impatiently. 'Unusually bright.'

'Yeah, but I was meanin' anythin' unusual a bit nearer home,' said Hagrid. 'So yeh haven't noticed anythin' strange?'

Yet again, Ronan took a while to answer. At last, he said, 'The Forest hides many secrets.'

A movement in the trees behind Ronan made Hagrid raise his bow again, but it was only a second centaur, black-haired and -bodied and wilder-looking than Ronan.

'Hullo, Bane,' said Hagrid. 'All right?'

'Good evening, Hagrid, I hope you are well?'

'Well enough. Look, I've jus' bin askin' Ronan, you seen anythin' odd in here lately? Only there's a unicorn bin injured would yeh know anythin' about it?'

Bane walked over to stand next to Ronan. He looked skywards.

'Mars is bright tonight,' he said simply.

'We've heard,' said Hagrid grumpily. 'Well, if either of you do see anythin', let me know, won't yeh? We'll be off, then.'

Harry and Hermione followed him out of the clearing, staring over their shoulders at Ronan and Bane until the trees blocked their view.

'Never,' said Hagrid irritably, 'try an' get a straight answer out of a centaur. Ruddy star-gazers. Not interested in anythin' closer'n the moon.'

'Are there many of them in here?' asked Hermione.

'Oh, a fair few ... Keep themselves to themselves mostly, but they're good enough about turnin' up if ever I want a word. They're deep, mind, centaurs ... they know things ... jus' don' let on much.'

'D'you think that was a centaur we heard earlier?' said Harry.

'Did that sound like hooves to you? Nah, if yeh ask me, that was what's bin killin' the unicorns never heard anythin' like it before.'

They walked on through the dense, dark trees. Harry kept looking nervously over his shoulder. He had the nasty feeling they were being watched. He was very glad they had Hagrid and his crossbow with them. They had just passed a bend in the path when Hermione grabbed Hagrid's arm.

'Hagrid! Look! Red sparks, the others are in trouble!'

'You two wait here!' Hagrid shouted. 'Stay on the path, I'll come back for yeh!'

They heard him crashing away through the undergrowth and stood looking at each other, very scared, until they couldn't hear anything but the rustling of leaves around them.

'You don't think they've been hurt, do you?' whispered Hermione.

'I don't care if Malfoy has, but if something's got Neville ... It's our fault he's here in the first place.'

The minutes dragged by. Their ears seemed sharper than usual. Harry's seemed to be picking up every sigh of the wind, every cracking twig. What was going on? Where were the others?

At last, a great crunching noise announced Hagrid's return. Malfoy, Neville and Fang were with him. Hagrid was fuming. Malfoy, it seemed, had sneaked up behind Neville and grabbed him for a joke. Neville had panicked and sent up the sparks.

'We'll be lucky ter catch anythin' now, with the racket you two were makin'. Right, we're changin' groups Neville, you stay with me an' Hermione, Harry, you go with Fang an' this idiot. I'm sorry,' Hagrid added in a whisper to Harry, 'but he'll have a harder time frightenin' you, an' we've gotta get this done.'

So Harry set off into the heart of the Forest with Malfoy and Fang. They walked for nearly half an hour, deeper and deeper into the Forest, until the path became almost impossible to follow because the trees were so thick. Harry thought the blood seemed to be getting thicker. There were splashes on the roots of a tree, as though the poor creature had been thrashing around in pain close by. Harry could see a clearing ahead, through the tangled branches of an ancient oak.

'Look ' he murmured, holding out his arm to stop Malfoy.

Something bright white was gleaming on the ground. They inched closer.

It was the unicorn all right, and it was dead. Harry had never seen anything so beautiful and sad. Its long slender legs were stuck out at odd angles where it had fallen and its mane was spread pearly white on the dark leaves.

Harry had taken one step towards it when a slithering sound made him freeze where he stood. A bush on the edge of the clearing quivered ... Then, out of the shadows, a hooded figure came crawling across the ground like some stalking beast. Harry, Malfoy and Fang stood transfixed. The cloaked figure reached the unicorn, it lowered its head over the wound in the animal's side, and began to drink its blood.

'AAAAAAAAAAARGH!'

Malfoy let out a terrible scream and bolted so did Fang. The hooded figure raised its head and looked right at Harry unicorn blood was dribbling down its front. It got to its feet and came swiftly towards him he couldn't move for fear.

Then a pain pierced his head like he'd never felt before, it was as though his scar was on fire half-blinded, he staggered backwards. He heard hooves behind him, galloping, and something jumped clean over him, charging at the figure.

The pain in Harry's head was so bad he fell to his knees. It took a minute or two to pass. When he looked up, the figure had gone. A centaur was standing over him, not Ronan or Bane; this one looked younger; he had white-blond hair and a palomino body.

'Are you all right?' said the centaur, pulling Harry to his feet.

'Yes thank you what was that?'

The centaur didn't answer. He had astonishingly blue eyes, like pale sapphires. He looked carefully at Harry, his eyes lingering on the scar which stood out, livid, on Harry's forehead.

'You are the Potter boy,' he said. 'You had better get back to Hagrid. The Forest is not safe at this time especially for you. Can you ride? It will be quicker this way.

'My name is Firenze,' he added, as he lowered himself on to his front legs so that Harry could clamber on to his back.

There was suddenly a sound of more galloping from the other side of the clearing. Ronan and Bane came bursting through the trees, their flanks heaving and sweaty.

'Firenze!' Bane thundered. 'What are you doing? You have a human on your back! Have you no shame? Are you a common mule?'

'Do you realise who this is?' said Firenze. 'This is the Potter boy. The quicker he leaves this Forest, the better.'

'What have you been telling him?' growled Bane. 'Remember, Firenze, we are sworn not to set ourselves against the heavens. Have we not read what is to come in the movements of the planets?'

Ronan pawed the ground nervously.

'I'm sure Firenze thought he was acting for the best,' he said, in his gloomy voice.

Bane kicked his back legs in anger.

'For the best! What is that to do with us? Centaurs are concerned with what has been foretold! It is not our business to run around like donkeys after stray humans in our Forest!'

Firenze suddenly reared on to his hind legs in anger, so that Harry had to grab his shoulders to stay on.

'Do you not see that unicorn?' Firenze bellowed at Bane. 'Do you not understand why it was killed? Or have the planets not let you in on that secret? I set myself against what is lurking in this Forest, Bane, yes, with humans alongside me if I must.'

And Firenze whisked around; with Harry clutching on as best he could, they plunged off into the trees, leaving Ronan and Bane behind them.

Harry didn't have a clue what was going on.

'Why's Bane so angry?' he asked. 'What was that thing you saved me from, anyway?'

Firenze slowed to a walk, warned Harry to keep his head bowed in case of low-hanging branches but did not answer Harry's question. They made their way through the trees in silence for so long that Harry thought Firenze didn't want to talk to him any more. They were passing through a particularly dense patch of trees, however, when Firenze suddenly stopped.