"Lost in thoughts, Harry?"

Harry looked up, dazed, from his reverie. He had found a secluded spot under a white willow tree on the Hogwarts grounds where he could sit and think for a while. Its leaves, so silver-white in summer, had turned to gold in autumn, but now most of the golden leaves had fallen from the tree. The ground was chilly this time of year, but Harry didn't mind.

Professor Lupin stood next to him, grey and ragged as always. "Are you worried about Sirius Black?" he asked gently as he sat down next to Harry under the tree. "I think everyone was quite shaken up by last night's violent attack on the portrait of the Fat Lady. It's difficult to believe that anyone could feel such rage against a mere portrait."

Harry recalled the slashed canvas he had seen the night before, so furiously torn to pieces, and he shuddered a little. Poor Mrs. Gryffindor! "Professor Lupin, do you think it would be possible to harm a portrait? Not just the canvas, but the person in it? I know that the Fat Lady escaped to another portrait, but what if she hadn't? Would she have been hurt?"

Lupin thought for a moment. "I don't know, Harry. I shouldn't think so. A person in a portrait is not a real person after all, merely a memory of someone who once was. How could you hurt a memory?"

"Oh, I don't know." Harry's voice sank to a whisper. "Memory charms could delete a person from everyone's remembrance, couldn't they?"

Lupin looked surprised. "I suppose so. But neither a person in a portrait nor a person in our recollection is really a human being, you know; memories are mere echoes of the real person. Although I suppose a memory can seem real enough at times..."

He smiled. "You are something of a portrait of James yourself, you know, but with a touch of Lily as well. It's so odd to see you sitting here; James used to sit under this very tree. You are so much like him, Harry. Sometimes I have to remind myself that you are not James come back to life again."

Harry looked up at the professor's tired face. How odd to think that Lupin's grey eyes had once rested upon his father's living face... Had Lupin and his father ever sat beneath this tree together, like he and Harry were sitting now?

"Professor," he said hesitantly, "I was wondering if you could tell me if there is a way to bring a person back to life after they are gone." He heard a little sigh escape Lupin's lips and felt a gentle hand on his arm, and he hastened to add: "Oh, I don't mean my parents, Professor. I am not trying to find a way to bring them back or anything like that. This is just… an old puzzle that I came across, a sort of riddle."

"Oh, like in a book?" Lupin smiled. "I used to enjoy those books of riddles and enigmas when I was a boy. Let's hear it, then, Harry."

Harry thought for a moment. "Suppose… suppose a person disappears at age 11. He or she vanishes so completely that no one can even remember that person any more. Then he or she shows up many years later, still eleven years old. A week later the person disappears again, and no one can remember that person any more. How can this be?"

"Hmmm." There was a pensive frown on Lupin's face as he considered the riddle. "Is this person human?"

Harry nodded. "Yes, he or she is human. But still a little different from other humans."

"Mmm. Now, this is a tricky one." Lupin's face wrinkled in thought. "Why would no one remember him after he disappeared? Did others see him before he disappeared?"

"Yes."

"I see. Is he a ghost?"

"No, not a ghost. The person is human."

Lupin smiled. "This is a most intriguing puzzle, Harry. I suppose some memory charm must be involved; that would explain how others could forget about his existence. But how could a human return after many years and be exactly the same age? Was there time travel involved? Or perhaps he drank the elixir of life? Maybe he found the sorcerer's stone?"

Harry recalled his encounter with the two-faced Quirrell in the underground chamber and shuddered.

"But why did the person disappear, then? Why would someone be erased from all recollection?"

Lupin considered. Then he grinned. "Ah. I think I have found the answer to your puzzle, Harry. You had me quite confused there for a while. The age doesn't quite fit, but otherwise the answer is quite obvious. Harry, this puzzle is about Lord Voldemort isn't it?"

"About Voldemort?" Harry stared at Lupin. "You think Voldemort made the person disappear?"

Lupin shook his head. "No, I'm not saying that Voldemort was behind the disappearance; I'm saying that he was the one who disappeared."

"The person who vanished was Voldemort himself?" Harry stared at Lupin, his heart filled with a sudden dread. No, impossible!

"Well, either Voldemort himself or someone very much like him. I think the point of the riddle is that someone had tried to make himself immortal, which explains the two appearances many years apart. But because that person's actions were unnatural and evil, someone else decided, after that first person's plans had somehow been thwarted, to erase all memories of what had happened. After all, Harry, if Lord Voldemort had succeeded in making himself immortal by means of the sorcerer's stone, and you then defeated him somehow, would you not consider erasing every memory of both him and his actions? Juts to make sure that no one else ever got a similar idea?"

Harry's mouth was so dry that it was difficult to speak. "Perhaps I would."

But Sally-Anne was not Voldemort, she was just a child, he thought desperately, just an ordinary little girl. Surely she could never turn into a dread figure like Voldemort? Could she have made herself eternal, and then turned into such a dark figure of horror that a kind soul decided, once she was vanquished, to erase her from all recollection?

No. No, the Sorting Hat said that there was no evil in Sally-Anne. Harry found comfort in his recollection of the Sorting Hat's confident assertion that Sally-Anne was just an ordinary little girl. But something whispered, darkly, in his mind: But wasn't Tom Riddle once an ordinary boy as well?

He shook the odd thought out of his head and went to the Great Hall for tea, accompanied by Lupin. As they parted inside the hall and went to their separate tables, Lupin smiled fondly at him: "See you later, James." He did not appear to notice that he had used the wrong name, and Harry did not point it out to him.

Harry stood by the window and looked out at the snow-covered landscape. The familiar statues and bushes looked strangely different under the thick layer of snow. Was that the shape of a gargoyle or an angel? He suddenly found it hard to recall. How difficult it is to remember clearly; our memories are obscured by our forgetfulness, until only the outlines remain...

He was waiting for Hermione, a piece of parchment clutched in his hand. The map! The legendary magical map of Hogwarts was real, and he was holding it! It had indeed fallen into the wrong hands: The pale, freckled hands of Fred and George. Who knew what kinds of pranks they had pulled off by means of this fantastic map that allowed them to trace the movements of teachers and students through the halls of Hogwarts? Harry smiled a little at the thought. The would have known when the coast was clear and when it just appeared to be. If you could see all authority figures on a map, you could also see where they were not and identify spaces open for mischief. But the twins had taken pity on Harry, who had become the Prisoner of Hogwarts every Hogsmeade day. They had decided, generously, that his need for freedom was greater than their urge to wreak havoc, and they had given him the map. Harry had been able to sneak off to Hogsmeade through one of the secret tunnels shown on the map, and he had learned the truth about his godfather Sirius Black, his parents' false friend... He shuddered.

He had spent hours already staring at the tiny moving dots on the map. How many of them there were, and how difficult it was to make them all out! In some places, where many people gathered, the dots became a blur; names were piled on names until the letters became a tangled mass without meaning. The solitary dots were easier to follow. He could see Hermione now, coming up the stairs to the common room, pausing for a moment midway up the staircase. Harry frowned. Why did she suddenly stop? Oh, the portrait of course! She was speaking to Sir Cadogan, who had gallantly taken over until the Fat Lady had time to recover. But on the map, it appeared that Hermione was standing there alone.

Where was Ron? Harry scanned the map until he found Ron's dot, in a large group of boys out on the grounds. The dots were moving back and forth - perhaps they were playing with a ball? Someone named Peter something-or-the-other was apparently determined not to let Ron get the ball, for his dot remained doggedly right over Ron's.

Hermione entered the common room and flung her schoolbag down. The loud thud it made as it hit the floor made Harry suspect that it contained the usual two dozen books or so. Harry looked at the map: They were indeed the only two people in the common room.

"Dobby?" He spoke into the air while staring intently at the dots in the kitchen. There were so many of them that the names attached to them were quite unreadable. One dot emitted a brief flash and vanished, and a new dot appeared next to his own in the common room.

"Harry Potter called?" Dobby was by his side, still holding a potato peeler in one hand, a graceful curl of potato peel dangling from it. He must have been helping with dinner. Hermione took it gently from him and put it down.

The three of them huddled around the map, watching the dots float across the parchment. The movements of the dots formed intricate and beautiful dark patterns across the yellowed parchment, and Harry suddenly felt as if he was looking at some abstract work of art. Each dot is part of a larger pattern, he thought, but he realized as he looked that the patterns themselves were fleeting, illusory, always changing.

There was Lupin under the tree, and there was Dumbledore in his office. Peeves was in Mr. Filch's office, perhaps being berated for some recent misbehavior. But Peeves' dot kept moving back and forth, so clearly he wasn't listening very closely. Wait, why was Peeves on the map?

"Look!" He pointed Peeves' dot out to Dobby and Hermione. "There's Peeves! But I thought ghosts didn't show up on the map..."

"They don't," said Hermione thoughtfully. "Look over here. I passed Nearly-Headless Nick on the stairs, but he is not on the map. Neither are the other ghosts. See, Moaning Myrtle does not appear in the bathroom. But Peeves is different; he is not a ghost, but a poltergeist. He is not the lingering memory of a person who once lived, but a different kind of creature altogether, a wild elemental being who thrives on chaos. Oh, look, he appears to be attacking Mr. Filch-"

They all watched in silence as the dot marked Peeves jumped on top of the one that bore Filch's name, then whizzed in the direction of the astronomy tower. Filch's dot remained motionless for a moment, then moved slowly toward McGonagall's office, presumably to report the incident.

Harry began to look at the larger structures on the map, rather than the individual dots. Hogwarts, with all its familiar rooms, was there, but some parts were missing.

He pointed at the map. "The Chamber of Secrets should be right here, but it's not on the map because it's unplottable. I suppose there could be other unplottable rooms at Hogwarts as well..." A sudden thought struck him. "You don't suppose that Sally-Anne could be... there, do you? In the Chamber of Secrets?" He felt a chill at the thought.

But Hermione shook her head. "After what happened down there last year, the chamber was searched thoroughly. McGonagall told me about it. What if the basilisk had laid an egg down there or something? There was nothing there, Harry, apart from a dead basilisk."

"How'd they get in there anyway? I thought I was the only Parseltongue in school; how did they open the chamber?"

Hermione shrugged. "Apparently, you had left in partly open." She pointed at the owlery. "Look at this; the owls don't show up on the map, do they? So you can't use the map to find a lost pet... As the ghosts told us, animals have souls, but they still don't show up on the map because their true names are unknown, unplottable. Look, you can't see Fawkes in Dumbledore's office either."

"I wonder how the map can know everyone's names," said Harry thoughtfully.

"All names have magic," said Hermione. "There is a magical connection between a person and his or her name. It's the same sort of magic that makes spells possible. For example..."

She fished her wand out of her pocket and waved it gracefully in the air.

"Papilio!"

A delicate lavender butterfly flew from her wand, its fragile wings so thin they were almost transparent. It fluttered round the room for a moment, then settled on the back of a chair. It remained there for a moment before fading and slowly dissolving into nothingness.

"Spells are essential to magic itself," said Hermione softly, "because of the magical connection between names and reality. I can say Papilio and conjure up an imitation of a butterfly, but I can't use the same spell to conjure up a bird. Even a wordless spell requires that you say the spell in your mind. Names are magic."

"Perhaps," whispered Dobby, "that is why wizards will only allow house-elves to have one name, instead of two."

Hermione drew her breath and stared, bewitched, at the dots congregated in the kitchen. It was almost impossible to make out individual names in the chaos of moving dots, but the blurry names, one on top of the other, were clearly shorter than the ones they saw elsewhere on the map. Harry had a feeling that Hermione would soon see to it that house-elves were informed of their right to carry a second name as well. But which names would those be? The names of their masters? That didn't seem right. Perhaps they would all have an X after their names to indicate that their last names had been robbed from them. Like Malcolm X. Dobby X... Harry rather liked the idea.

"At least the house-elves are on the map," said Dobby cheerfully. "But animals and ghosts and portraits are not."

"Neither is the Sorting Hat," said Hermione, scrutinizing Dumbledore's office. "I don't think it really has a soul; it is just the ambitions and discernment of the four founders concentrated into one magical object."

Harry stood for a moment, lost in thought. Then he said: "I wonder what would happen if someone changed their name? When Tom Riddle became Voldemort, did his dot change names as well? If he came into the castle now, would his dot say Tom Riddle or Voldemort, I wonder?"

"I suppose," said Hermione, her voice shaking a little, "that it would depend on whether his soul had been transformed as well as his name."

She stared fixedly at the map. "Oh, there's Ron again. Seriously, is he in love with that Peter person? They seem completely inseparable. What's his last name? Petrie... No, I can't read it. It's amazing how much information this map contains." She fingered the golden chain around her neck. "If only there was a way to turn this map back to the day we were sorted..."

"Try it!" said Harry eagerly.

Hermione looked doubtful. She pulled out the golden time turner, removed it from her neck and held it over the map. Slowly, she turned the golden clockwork a little. No change could be seen on the map.

"Dobby thinks it would work better if it touched the map, Miss."

Hermione looked at the little house-elf for a moment. "Good idea, Dobby," she whispered. "Perhaps you two can hold the map while I spin the clockwork..."

Harry and Dobby held the parchment horizontally between them, and Hermione placed the time turner directly underneath the map, touching the parchment. Then she began to turn the dial.

It was working! Suddenly the little dots began to move in furious bursts of speed. Time was rewinding before their eyes.

"How do we know what time it is?" asked Harry bewildered. "On the map, I mean?"

"Look carefully," said Hermione evenly. "The brief moments when the dots are not moving are nights. And look, now the castle is almost empty; all the students have left. This must be last summer, when everyone went home. Now we are back in our second year; that's Mr. and Mrs. Weasley hugging Ginny after the ordeal in the Chamber of Secrets. See, your dot disappeared from the map; you are in the chamber of secrets. And that's you and Ron in the Slytherin common room talking to Malfoy. Good thing he didn't have this map, or he would have known you weren't Crabbe and Goyle! And there I am in the bathroom..."

Harry stared at Hermione's dot. He recalled her horror at being partially transformed into a cat by the Polyjuice potion. But the map wasn't fooled; her dot was still clearly marked "Hermione Granger".

"Oh, look, there's Dobby, and there's Colin Creevey's dot following yours around, Harry. And this must be Christmas, because the castle is much emptier... And this is Halloween, look at us in the dungeon for the Deathday party..."

Harry looked at the dungeon. He remembered Nearly-Headless Nick's Deathday party, attended by scores of ghosts, and yet the map showed no party, simply three dots wandering aimlessly in a dungeon.

"Oh, my goodness!" Hermione sounded startled. "The Whomping Willow really did give you and Ron a beating, didn't it"

Harry looked at the two dots marked "Harry Potter" and "Ronald Weasley" rattling mysteriously back and forth right outside the castle. The Whomping Willow was not on the map, of course, and neither was the flying car.

"Summer again" said Hermione softly. "Oh. Look at McGonagall, how much time she spends in the library over the summer! And now we are back in our first year." A shaky little gasp escaped her. "Look at Quirrell... His dot has a strange sort of superscript on it..."

Harry saw that Quirrell's name had another attached to it, a minuscule name above the first, written so close to the name "Quirrell" that the letters were touching, merging: "Voldemort".

"You were right, Harry," Hermione whispered. "I suppose Tom Riddle really did change so completely that his soul was transformed as well. The map recognizes him as "You-Know-Who"..."

"No, it doesn't," said Harry, slightly irritated. "The map has the courage to use his real name."

Hermione ignored him and went on: "Oh, that's you talking to Dumbledore, Harry. It must be Christmas; the castle in almost empty. And there's your dot looking a little blurry - you must have been wearing your Invisibility Cloak. Oh, and this is Halloween, let's go slowly, so we don't go back too far and miss the sorting. There I am in the bathroom... The troll had a name? Well, well, well..." They stared at the map as Harry and Ron's dots attacked a dot marked "Thrivaldi".

"There we are, going to Hagrid's for tea," said Hermione breathlessly. "Pay attention now - the previous day was the sorting. This is the night before, and here's the welcoming feast. There were are at the house tables. I can't see Sally-Anne at the Hufflepuff table, can you? I see Susan Bones and Hannah Abbot - why isn't she with them? Oh, this is the Sorting. Look, that's you being sorted, Harry! Your dot is by itself in the front. And... why is nothing happening? I don't remember a pause between sortings. And that's Parvati Patil being sorted, and that's Padma..." Hermione's voice trailed off.

The three of them stared at the map, at the sea of dots and names. There was no dot marked "Sally-Anne Perks", only a small empty spot at the Hufflepuff table between Susan Bones and Hannah Abbott where Sally-Anne should have been.