'But … ' There was a sinking feeling in Harry's stomach. The girl had called his father Potter, but in a haughty tone that clearly showed how much she disliked his father. Why did everyone he had met so far dislike him so much? He had no idea why Lily did, but Snape was a different matter. The words Lupin had said to him a few hours ago (was it a few hours ago?) about Snape came to his ears: 'We were in the same year, you know, and we – er – didn't like each other very much. He especially disliked James. Jealous, I think, of James's talent on the Quidditch pitch … '

And another recollection swam to the front of his mind against his will and stayed there; a picture of himself and an adult Snape – Snape had found the Marauder's Map and was sneering at Harry, trying to provoke him into telling the truth …

'How extraordinarily like your father you are, Potter … He, too, was exceedingly arrogant … Strutting around the place with his friends and admirers … the resemblance between you is uncanny …'

And what had he said in return? Harry winced as he remembered his own defiant answer.

'My dad didn't strut. And neither do I.'

But how could he be so sure? How could he know that his father hadn't been an arrogant prat, the way Snape had always told him? Dumbledore, Hagrid, Sirius and Lupin had all given him glowing reports of his father … but Sirius and Lupin were James's friends, after all, Harry thought with a pang … maybe they were just biased in favour of him …

Was that why Snape hated James so much? Not because he just did, but because James was so popular, because James had bullied him, the way Harry had seen him bully the round-faced Slytherin boy in the Great Hall?

You're just jumping to conclusions, Harry told himself desperately, trying to quash the rising doubts in his mind. Lupin had said that James and Sirius had been the height of cool, surely it had only been Snape and Lily who really disliked them …

And what about Snape? The adult Snape loathed him as much as Harry hated him back, didn't he, always picking on him in class and calling him an attention-seeking, arrogant prat? The Snape Harry had met just half an hour ago did not know who he, Harry, really was, and seemed to even like Harry and Hermione, whom he had offered to help. He did not know what to think.

'Harry, come on,' called Snape, tearing along ahead of him, dragging a confused Lily by his side as he raced along corridors. Harry followed dazedly; it felt very strange to be called in such a friendly manner by one whom he considered an enemy (admittedly, Snape did not know who he was). It felt even stranger that, as much as he hated Snape, he couldn't help liking this boy. If he didn't know better, he would have thought that it was all a very strange dream, and that he would wake up in the hospital wing with Hermione any minute. And Ron, complete with a broken leg …

When they reached the seventh floor, Snape stopped, waited for Harry and Hermione to catch up, and then, ignoring their pants and wheezes, strode over to the wall opposite a tapestry of Barnabas the Barmy, and asked Harry confidently, 'What would you like?'

'Wha–– what d'you mean?' said Harry. 'What are you talking about?'

'I mean – what do you want? You two'll need somewhere to stay the night, and – '

'Hang on,' interrupted Harry. 'You're not saying that this is the door to the Room of Reduction or whatever it is?' He gestured to the tapestry of Barnabas the Barmy.

'The Room of Requirement. And this is the door,' Snape said cryptically, nodding at the blank wall on the other side.

Harry squinted at it. 'You're having me on,' he said finally.

'No, he's not,' interjected Lily. 'It really is. I'll show you it if – '

'"If" what?'

The last words came out in a rush. 'If you swear not to tell anybody about it. And that includes Potter, Black, Lupin and Pettigrew.'

'The makers of the Marauder's Map?' Harry said, before he could stop himself.

'The what?' Snape looked suspicious.

'Never mind,' Hermione said. 'All right, so we sw––'

'What are you doing?' Harry mouthed at her, out of the corner of his mouth, so that Snape and Lily wouldn't see.

Hermione shot him a meaningful look and flexed her left wrist slightly, flicking the face of her watch towards him. Harry understood this to mean, 'We haven't got much time.'

'OK,' he said hurriedly, with the uncomfortable feeling that he would regret this promise later. 'We swear – now show us the room.'

Snape seemed to enjoy having Harry and Hermione depend on him. He whispered something to Lily, and together they paced back and forth three times in front of the blank wall, amid Harry and Hermione's obvious confusion. Harry was just about to ask Snape what in the wizarding world he was doing, when an ornately carved door suddenly materialised in the space where, seconds before, there had been an expanse of empty wall.

'This,' Snape said, grabbing the shiny brass doorknob and wrenching the door open to reveal an enormous room, very like a dormitory, with two four-poster beds complete with bedside tables and tapestries hanging on the walls, 'is the Room of Requirement.' He stood aside for Lily to enter, and then waited as Harry and Hermione scrambled in, shutting the door behind them.

Harry suddenly realised that his mouth had dropped open in astonishment. Hurriedly, he closed it again.

'But – this is brilliant!' Hermione cried, walking around. 'How did you do this?' She lifted her arm and made a sweeping motion, gesturing to the whole room.

'No problem,' Lily said cheerfully, regaining her voice as she studied the Room. 'It's the Room of Requirement – just ask it what you want, and it'll appear. Nothing to it.'

Out of the corner of his eye, Harry saw a gigantic floor-to-ceiling bookcase filled with books of all shapes and sizes appear against the wall just in front of Hermione. He heard her very audible gasp.

'See?' Lily said, as Hermione, her face glowing, began to inspect the books. 'We've made it so that only people you trust can come in here – so right now, Severus and I can come in. Also, the only thing the Room doesn't produce is food, so we'll have to figure out a way to smuggle you two some.'

'How did you find out about this room?' Harry asked curiously, talking more to Snape than Lily.

Snape turned crimson, but his voice was steady as he answered, 'Potter and his mates were chasing me last year, and I was thinking that I needed somewhere to get away from them – and the door appeared.' He looked suddenly defensive and sulky.

Harry's stomach gave a queer lurch. He wished he hadn't asked. 'So they didn't find you?' he said, without really thinking about what he was saying. His voice sounded like it was coming from far away.

'What do you think?' Snape snapped. 'Of course they didn't! They don't even know about the Room – but we don't want to take any chances. That's why we made you two swear.' His face contorted suddenly for a moment, giving Harry a mental image of his older self.

'Anyway,' Lily said briskly, thinking for a moment and then glancing at a clock that appeared almost immediately on the wall, 'Sev and I've got to get going, or we'll be in trouble for being out late.' Snape followed her to the door, and they left.