At 0645 on Monday morning, Oliver Wood on his way to an early morning run found Argus Filch petrified in a corridor near the Entrance Hall. Summoned by McGonagal, Snape arrived to find the rest of the Heads of House inspecting the bizarre statue.

Whatever had happened had occurred while the caretaker was taking a swig from an enormous bottle of Muggle Scotch, fire whisky having no effect on those without at least a measure of magic in them. The expression of his face was one of utmost horror, but scarcely less alarming was the message scrawled on a nearby wall in what had looked like blood but which later turned out to be red paint from the art room.

THE CHAMBER OF SECRETS IS OPEN

MUDBLOODS AND OTHER FILTH BEWARE

"I've closed the corridor, we've got to get him to the infirmary before the pupils see him," said McGonagall. "What a day for the Headmaster to be away." She waved her wand and conjured a huge dust-sheet and draped it over the stony figure.

"I'll take care of the levitation, you go and keep them away," said Snape. Flitwick and Sprout hurried off as he tilted the bizarre bundle sideways and headed towards one of the private staff corridors the pupils were not supposed to know about. "Where is Albus anyway?"

Minerva held the door open as he carefully manoeuvred Filch round a tight corner. "Lobbying for Arthur Weasley's Muggle Protection Act – Lucius Malfoy is trying to kill it in the Oversight Committee. I'll message him immediately but I don't know when he'll be back, possibly not until tonight. I'm going to confine the pupils to their common rooms after breakfast and then we can search the school."

The search found nothing except that Hagrid's rooster had been killed in the night, which reminded Snape of something but he couldn't bring whatever it was to mind. Not that it mattered, when there was something loose in the castle itself, a fox or polecat getting in from the Forbidden Forest was the least of their worries.

The pupils knew something was up, even if their guesses were wide of the mark. There was still no sign of Mrs Norris and some of the teachers were half convinced it might be a prank got out of hand – no one in the castle had any love for Filch or his cat.

As the day wore on it grew steadily more irritating. The pupils were on edge through ignorance, the teachers were on edge through all too much information and the whole Voldemort business was still bubbling underneath everything. Draco Malfoy tried to throw his weight and name around and ended up with a bloody nose when the third year Hufflepuff he was trying to impress completely lost his temper. Snape was so fed up with the little toe-rag he could have given the Hufflepuff a couple of chocolate frogs, but was obliged to give him detention instead. If he asked Sprout to supervise, the boy wouldn't be too severely punished and he might get a few tips on how not to haul off at mouthy brats at the same time.

And to cap it all, Lupin was not at all bothered about being asked to give The Talk to a bunch of spotty, walking hormone factories. There was very little point in coming up with a really subtle revenge if the revengee wasn't the slightest bit fazed. Personally, Snape could think of few things worse; Lupin merely nodded and asked which years he should talk to first.

Although he would have fiercely denied it, Snape was relieved when the Headmaster returned just before dinner that night. The rest of them had run out of things they could think of to do and were reduced to sitting round the Staff Room rehashing old legends about The Chamber of Secrets. Not one of them thought the Chamber had actually been opened, it was merely one of the school legends like the swimming pool which was supposed to exist on one of the upper floors or the house elf ghost which every first year for the last 50 had been convinced haunted a storeroom in the cellars. What no one said, and everyone thought, was what a piece of luck it had been that it was Filch and not a pupil who had been out in the night and had met whatever it was.

To absolutely no one's surprise, the news was all round the school the next morning. The Headmaster made an announcement at breakfast that pupils would be escorted to and from their classes and that after dinner, everyone would stay in their common rooms. A hundred voices rose in complaint and question but there was no choice for it.

The only cheering thing that happened for the next few days was the sight of Harry waiting outside Minerva's classroom, consciously relaxing in an obvious attempt at occlumantic mindfulness. He did wonder if the boy was hearing something at that moment, but when he raised an eyebrow, Harry shook his head and smiled sunnily.

Nothing further happened that week. Lupin, Snape and the Headmaster had a brief meeting about advancing their anti-Voldemort agenda, but decided to wait a little longer. The school was too upset and edgy to risk further information being lost in the hubbub.

On Saturday, Harry arrived in a huff with his hands full of holey socks, far too far gone to attempt reparo.

"How on earth did they get in this state?" asked Snape over tea and ginger snaps.

Harry squirmed a little and then admitted to wandering around the stone floors of the dorm and common room in his stockinged feet. "I think I got into the habit with the Dursleys," he said. "My shoes never fit and they always said I was tracking dirt on to the carpets – even when I wasn't – so I got used to taking them off. I've got some of my pocket money left." He dug in a pocket and produced a handful of coins."Is there some way I can get some more? Percy says these are past it."

Snape took the coins, sorted out a galleon and a couple of sickles and handed the rest back. "And I suppose you forgot about your slippers. I'll take the money, it'll teach you not to be so careless in future. I'll order you half a dozen pairs if you promise to remember in future."

Harry nodded. "Sorry, it's just I've never had slippers before." He sipped his tea. "Professor?"

"Hm?"

"How do you buy things? I mean, Aunt Petunia used to order things from catalogues – do wizards have them too?"

"One can buy things by owl order although in this instance I shall merely pop into Hogsmeade, I need some things for myself."

Harry considered this for a moment. "It's Ron's birthday soon – I want to buy him a present." He looked into his teacup. "I'd like to get him something nice, he says everything he has is rubbish, even his pet rat has a toe missing. Are there catalogues for that sort of thing?"

Snape didn't like the sound of that one little bit. "Did Weasley ask you to get him something?"

Harry was adamant. "Oh no, it's nothing like that. It's just... well I got that wicked flute from you and I really love it, and Ron sings just as nice as me and I know he wishes he had one too."

"Harry, Mr Weasley comes from a large family, you can't possibly make up for everything his parents can't afford to buy him. Pity is not a sound basis for friendship."

"I don't pity him!" said Harry indignantly. "Why would I? He's got that great family, all those brothers and a sister and his Mum made me a jumper just because Ron told her I didn't think I'd get any presents. He's so lucky!"

"Ah." Snape sat for a moment. This would require careful handling. "Have you told Mr Weasley that?"

"Um...no?" Harry was looking worried again, so Snape decided to keep it simple.

"I don't think it's a good idea to buy Mr Weasley an expensive present like a flute. It will only make him feel ashamed. I suggest that, when his birthday comes, you let me buy a recorder for him." Harry opened his mouth to object but Snape continued. "Yes, we can use your pocket money. I think a recorder will give Mr Weasley a chance to decide if he has any aptitude and you can teach him enough to get started. If in the Summer you believe he has demonstrated enough dedication and willingness to learn, you can both look into finding a second-hand instrument for him."

Harry demonstrated he had learned not to rush into argument by thinking for a couple of minutes, dunking his ginger snap for so long that half fell off into the cup. "Do you really think he'd be ashamed?"

"Yes I do. Not right away but once he has had chance to think about it." Snape summoned his courage, he had promised honesty for the boy – even if he had only promised himself. "I was a poor boy at school and though I was glad to get gifts from those with more money, things like books and clothes, I always resented the people who gave them to me." Admittedly, the people who gave him things expected favours in return, but that was a subtlety Harry would probably not understand yet. "In the meantime, I want you to do something for me, Harry."

"Yes?"

"Next time Mr Weasley complains, tell him how lucky he is and keep telling him." Gryffindors, he reminded himself. "I don't mean keep on nagging him about it. Just make sure that he knows how much he has and how much you wish you had too."

"Okay," said Harry, dubiously. "If you think it will help."

"We both know family is important because we don't have any. Mr Weasley might not realise as yet, just how lucky he is. It might make it easier for him to accept his comparative monetary poverty if he remembers how rich he is in other ways."

Harry nodded slowly. "I thought it was a bit thick him complaining – he's got a Mum and Dad!" Then they were into checking his mindscape – floor was coming along, ceiling needed more work - and then it was more marking and more patrols. It was so mundane, he almost forgot the most recent danger.

Next morning Ron Weasley was found in the Charms corridor. He was bent over a window-ledge, although he were looking at something at the join between glass and wall; but his head was up and he was staring though the glass and his expression said he had seen something terrible.

On the wall were more letters:

ENEMIES OF THE HEIR BEWARE