After dinner, Professor Snape led the Slytherin pupils along yet another maze of underground passages before stopping at a blank stretch of stone wall. 'Observe,' he said. 'The common rooms to the other houses are guarded by portraits which demand passwords, or doors with talking knockers which ask riddles. What are the disadvantages to this? Potter?' he added, ignoring Icicle's waving hand.

Harry yawned. He had eaten rather too much at dinner, from roast beef and Yorkshire pudding to treacle tart and rice pudding, and he felt on the verge of turning into a pudding himself. 'We could be stuck out here if we can't answer the riddle?' he suggested.

'And?' demanded Snape.

'It'd get cold sleeping on the floor?'

'It'd get cold sleeping on the floor? Is that the worst problem your minuscule brain can imagine? You don't think that, for example, not being able to get out of the way of a stray Acromantula might be a greater inconvenience?'

'What's an Acromancer-thingy?' asked Harry. He knew his answer hadn't been a good one, and there were worse things than being cold – what if someone like Dudley came hunting him? – but how did Professor Snape expect him to know what the main dangers were at Hogwarts when he hadn't even heard of Hogwarts until a couple of months ago, and had never been here before?

'The sort of creature that a Gryffindor would think makes a good pet,' was all Professor Snape would say. 'Someone else, then – Malfoy,' he added, again ignoring Icicle. Apart from getting cold sleeping on the floor, what are the disadvantages of having a portrait or a talking doorknocker marking the entrance?'

'People from other houses can see where it is,' said Draco Malfoy primly.

'Exactly. Here, as you can see, there are no obvious signs that this stretch of wall is different to any other, but if you take note of the precise irregularities in the stonework, they will become familiar to you.' Professor Snape made each of the first-years stand in front of the patch of wall in turn, committing its markings to memory. Harry noticed a crack in the stone above him that looked like a snake. That would do for a landmark.

'Remember that the relevant stretch of wall will not always be in the same place,' Professor Snape continued. 'You will need to stay alert in looking out for it, wherever it appears. Now, what is another disadvantage of sentient portraits or doorknockers as guards? Weasley?'

Icicle Weasley looked relieved at being allowed to add something at last. 'They can be fooled,' he said.

'Precisely. Portraits are as eccentric as whoever was their subject was in life, or more so. Some are naïve enough to let in any stranger who can find out the correct password; others can be intimidated by the threat of paint-stripper. A guardian who asks riddles might let in anyone whose answer strikes it as clever, original, or amusing. This wall, by contrast, has no imagination, no fear, and absolutely no sense of humour. It does have a good enough visual memory to recognise who is or is not a member of Slytherin house, but, in case of intruders disguising themselves, it will also demand the password, which is currently – Rincewind!'

Icicle sniggered at this, while everyone else looked baffled. The hidden door slid open, revealing a long, low underground room with rough stone walls and ceiling, lit by green lamps hanging from chains. There were hard wooden chairs around the fireplace, with the backs decorated with knobbly carvings of strange beasts: dragons and snakes and three-headed snakes and something that looked like a cross between a pelican and a flying horse, and many more that Harry could not put a name to. He wondered how many of them really existed, and perhaps even lived in the grounds of Hogwarts. Mainly, though, he wondered why the common room couldn't have cosy armchairs and sofas.

Professor Snape gestured to all of them to sit. Harry felt a strange squirming behind him, and realised that the carved wooden dragon was giving him a massage. It felt much more pleasant than he had expected, and some of the tiredness left him as the dragon wriggled its long, snaky body – very different in shape from Toothless – against his shoulders.

'Welcome to Slytherin,' said Professor Snape. 'How many of you expected to be sorted into this house?'

Virtually everyone except Harry, Icicle, and Flint raised their hands.

'Oh?' said Professor Snape, rounding on Harry. 'And why not? Because you had been told that only evil people become Slytherins? Did you dream of being a heroic Gryffindor instead of a villainous Slytherin?'

'No!' said Harry angrily. 'I'd never heard of the houses or sorting until tonight, so how was I supposed to expect anything about which one I'd be in? All I knew was that when the hat started calling out who would be in what house, my friends were sorted into Ravenclaw and Gryffindor and Hufflepuff, so I thought maybe I'd be with one of them.'

'The people who were your friends,' Professor Snape corrected him.

'They're still my friends!' Harry retorted. 'Just 'cause we're in different houses doesn't have to change that!'

He felt awake enough by now to want to have an angry argument, but instead of being angry, Professor Snape just looked unbearably sad. 'Yes,' he said. 'When I was eleven, I used to believe that was possible, too.

'In theory, Hogwarts is divided into four houses. In practice, as even any first-years who were paying attention will have noticed, it is divided into two factions, one of which is three times the size of the other. As Slytherins, you will find that everyone in Hufflepuff, Ravenclaw, and particularly Gryffindor, will regard you as evil, disgusting, and beneath contempt, fit only to be used as target practice for their hexes. Therefore, as a matter of survival if nothing else, all of you have a responsibility to take care of each other, because no-one else will. Never be alone, or you will make yourself a target. Never accept anything that a member of another house offers you to eat or drink without testing it for concealed potions. And finally – you may know that Slytherin has a higher proportion of pure-blood wizards than the other houses. This does not mean that half-blood and Muggleborn Slytherins are any rightfully less members of this house. All of you are here because the hat chose you for Slytherin, and you will treat each other with respect and loyalty.'

'What if they're part troll?' drawled Draco, looking pointedly at Flint.

'Exactly the same applies.'

'Well, I suppose part-troll isn't as bad as part Squib accountant,' Draco conceded, turning his eyes to Icicle.

'I'd rather be either than the son of a cowardly Death Eater who wriggled out of going to Azkaban by pretending he'd been Imperiused and wasn't responsible for his actions,' retorted Icicle.

'SILENCE!' roared Snape. 'Have any of you imbeciles been paying attention to anything I've said?'

'Yeah, yeah,' yawned Draco. 'We need friends to watch our backs in case any of those scary Gryffindors sneak up behind us. Well, I've already got my two minions,' – he gestured to Vincent Crabbe and Gregory Goyle – 'and Potter doesn't think he needs friends in Slytherin because he's got friends in the other houses…'

'That's not true!' retorted Harry. 'I don't not want to be friends with you because you're a Slytherin. I just don't want to be friends with you, Draco, because I don't like you. Okay?'

'Yeah, lots of us don't like you,' Icicle chimed in.

'You really weren't listening, were you?' said Flint. 'It's not about liking each other or not. It's about needing to work together as a team. You're bickering like little kids, because you're tired and you've had too much sugar. So, everyone in third year and under, go to bed now, or you'll be in no shape for anything in the morning. We fourth and fifth years will be along in half an hour.'

Yawning and grumbling, the younger pupils made their way to the dormitories and fell asleep. Harry dreamed that he was re-taking his sorting, and this time pleaded with the hat, 'Not Slytherin. Not Slytherin.'

'Not Slytherin, eh?' said the hat. 'Well, in that case, better make it RAVENCLAW!' It turned into Professor Quirrell's turban, coming low over Harry's face and covering the scar on his forehead, except that Harry could feel that it wasn't just a scar but a second face, which hissed, 'Yesssss!' There was a flash of green light, and Harry woke up, screaming. His scar was searing with pain again, but he tried to stifle the scream. The others in the dormitory would laugh at him, he knew.

He felt something patting his hand. 'I'm all right,' he mumbled crossly. Sympathy would be even worse than being laughed at.

'Harry Potter is not all right,' said a squeaky voice. 'Harry Potter needs his friends. Dinky will take Harry Potter to his friends now.' A small hand grasped his more firmly, and Harry felt as if his body had been separated into atoms and sucked one by one through a wormhole. He emerged in a warm, candle-lit place which was obviously a kitchen. Dinky, the creature who had taken his hand, he could now see, was a humanoid who looked a bit like Yoda, but with bigger eyes. He – or she? – was even smaller than the goblins Harry had met at Gringotts (but a lot bigger than Twigleg), and wore a tea-towel tied around one shoulder and slung rakishly under the other arm. There were many more of these around, some washing dishes, others preparing food, including a dish involving smoked haddock, curry spices, hard-boiled eggs and rice, which smelled delicious even though it was obviously a long way off being ready. A few napped, snuggled together in big comfortable armchairs that looked the right size for a large human and could easily seat four or five snoring whatever-they-were.

Sitting on the floor beside a table which had obviously been built at Dinky-height rather than human height were Ben (with Twigleg on his shoulder), Hiccup (with Toothless snoring loudly on his lap), and Hermione Granger, the girl who had been sorted into Ravenclaw just before Twigleg. Ben and Twigleg looked cheerfully at home, if sleepy. Hiccup looked wide-eyed and curious. Granger looked shocked and indignant.

Dinky offered them tea and scones, even finding a thimble as a teacup for Twigleg. Everyone gratefully accepted except Hermione. Toothless woke up long enough to try to steal a piece of smoked haddock, but when the creature who was preparing it offered him some, he mouthed it for a moment, spat it out on the floor, and went back to sleep.

'Couldn't you sleep either?' Ben asked Harry.

'I did, at first. But I woke up, and, uh, Dinky decided I needed to come here.'

'Me, too,' said Hiccup. 'I was having a nightmare about my archnemesis.'

'Your cousin?'

'No, worse than Snotlout. Snotlout just wants me to die because we're rivals. And most of the predatory dragons I meet just want to eat me because I'm edible. But Alvin keeps trying to kill me because he wants revenge because he thinks everything in his life is my fault because, let's see… before he met me, a trap that had been laid over a hundred years ago by an ancestor of mine cut his hand off, and apparently being the descendant of Grimbeard the Ghastly means I inherit the blame for doing that; then when Alvin got eaten by a Strangulator because he'd trapped us in a cave while searching for treasure, Fishlegs and I didn't stop to cut him out of the Strangulator after I killed it because we assumed he was already dead; and then when he kidnapped us to force us to fight as gladiators and we had to escape in a balloon and he tried to climb up to the balloon to attack us, we threw him down. Every time you'd think he must be dead, he keeps coming back.'

'Like Nettlebrand,' said Twigleg. 'I still have nightmares about him, too.'

'So do I,' said Ben. 'Was that what woke you, tonight?'

'No, Master. I just couldn't sleep, with Toothless snoring. He snores even louder than the hobgoblins at home.'

Hermione glared at Ben. 'You keep house-elves like these to wait on you, too? And you expect Twigleg to call you "Master"?'

'Well, they're kobolds, but I think they're a slightly different species to Dinky and Lolly here,' said Ben. 'But they look more like these ones than like the goblins at Gringotts, or forest brownies like my friend Sorrel, or leprechauns or Dubidai.'

'Brownies is lazy!' snapped Dinky. 'They does one good turn a day, no more, if they works for humans. And most of them prefers dragons.'

'Why should you have to work for humans?' asked Hermione indignantly. 'Why should you have to work through the night?'

'House-elves likes the night,' said Dinky. 'Only a few of us has to work the day shift, poor souls,' he added, gesturing to the group curled up on the armchair. 'But we takes turns.'

'But why do you have to work for humans at all?' Hermione repeated.

'Not for humans – not here!' retorted Dinky. 'Some of us, yes, we belonged to wizards before – bad wizards. Some hurt us, made us hurt ourselves. Sometimes, was even given clothes, if masters very angry with us.' The elves looked sympathetically at those of their number who were wearing an item of human clothing – perhaps a hat or a vest – while the others wore scraps of cloth such as tea-towels or pillow-cases. Harry noticed that many of the elves had old scars or ragged ears, but they didn't seem to regard being tortured as nearly as terrible as being made to wear clothes. 'Others ran away from bad masters, came here, get Albus Dumbledore to buy us free from old masters.'

'But are you free? If Professor Dumbledore bought you, doesn't that mean he owns you, now?'

'No! Hogwarts house-elves does not belong to a man! Hogwarts house-elves belongs to the castle! Brownies belongs to the forest – most goblins does too, except the ones at Gringotts – Dubidai belongs to the mountains, nisses to farms, klabautermanns to ships, knockers to mines, and hobs and house-elves belongs to houses. Humans comes and goes, but house-elves belongs to here. And we belongs to each other. In a wizard's house, maybe just one house-elf. Here, we has our tribe.'

Hermione stayed to argue politics for a while longer, but all the other visitors were soon yawning. Harry fell asleep, and woke up to find himself back in his bed in the Slytherin dormitory. He might have thought the whole thing was a dream, if it hadn't been for the scone crumbs on his pyjamas.