Lupin raised his eyebrows at the bushy-haired third year standing nervously in the doorway of his office.

“A Memory Modification Charm?� he asked. “Why?�

“Just...just in case, you know...� Hermione said, wringing her hands. She needed to know this, in case of any number of things: in case Voldemort came back and she had to go into hiding; in case someone caught her using the Time Turner; in case something happened with Harry, as things so often were happening with Harry that involved blood and pain and fighting things beyond their magical experience.

Lupin did not look convinced. “You're not meant to learn the Memory Modification Charm until fifth year, Miss Granger,� he said quietly. “Does this have anything to do with the device you have around your neck?�

Hermione gasped and held her hand to her throat, feeling the fine gold chain around her collar. “How – no one is supposed to know about that!� she said.

“All the staff know, Miss Granger,� Lupin said, steepling his fingers and resting his elbows on the desk. “And I have to say,� he added, “that if any instance should arise in which you would need to use a Memory Modification Charm, you should not attempt it yourself, but inform the nearest professor immediately.� He frowned slightly.

“Oh, I would, I promise, this is just –“

“Just in case, yes, you've said,� he interrupted. “Well, as a teacher I can hardly deny an eager student the opportunity to learn, can I? Even if she wants to learn a spell far beyond her years.� He smiled slightly. “I am hardly the person to prohibit the learning of advanced magic.� His voice grew even softer on the last sentence, as though he were speaking to himself. His focus seemed to turn inward, or perhaps, Hermione thought, backward through time.

“Sir?� Hermione said tentatively, when a few moments had passed.

Lupin started and looked at her. “Yes,� he said, shaking his head as though trying to rid his mind of its thoughts. “Yes, I will teach you. I will need to procure a device, however...please stay here and wait while I see the headmaster. Oh, I will not tell him I am using it to teach you the charm,� Lupin added, seeing Hermione's alarmed look. He stood and crossed to the door; Hermione moved out of his way, into the office. “Please, sit down. There is chocolate in the tin if you would like to have any,� he said, indicating a tin box on the edge of his desk. “I shall return shortly.�

As Lupin walked down to the Defense Against the Dark Arts classroom and then into the corridor, Hermione sat down on one of the stiff wooden chairs cushioned with soft, dark green corduroy. She looked at a creature she recognized as a grindylow in a murky tank near one wall; it made faces at her and she glared at it. It swam a few laps of its tank upside down, eying Hermione, then disappeared into the gloomy water. Hermione opened the tin on Lupin's desk and saw several large pieces of what appeared to be Honeydukes' best chocolate, but her nerves kept her from really wanting any. She took a grateful sniff of the sweet aroma, then closed the box again.

A few minutes later, Lupin returned, closing the door of the classroom behind him. He was carrying a heavy-looking, shallow stone basin engraved with strange runes all around the rim. He beckoned for her to join him.

“A Pensieve,� he explained when she reached him. He had set the basin on one of the worn wooden desks near the back of the classroom. “This is the best and lowest-risk way to practice the Memory Modification Charm.� He touched the tip of his wand to his temple, then drew it away; a thin silver strand of what looked like hair came with it. It grew longer, longer – then broke, swirling down into the Pensieve. The shimmering light reflected off a dark window nearby.

Hermione stared into the basin, fascinated. “I've read about these!� she said breathlessly. “They can hold thoughts and – and replay them...� she said, trailing off as she realized she was doubtlessly saying what Lupin already knew about the object.

“That is correct,� Lupin said patiently, “and they not only replay them for their owner, but for anyone who happens to venture into the memory. In order for one to watch the memory in the Pensieve, one must duck down one's head -� Lupin leaned forward, partially demonstrating - “and put his or her face into the basin.�

Hermione looked discomfited by this news, but nodded in understanding.

“Now, Miss Granger, before we begin the charm, you will need to see this memory as it currently exists. It is a recent one – and a rather boring one, I'm afraid,� Lupin said, smiling. “It is the day I stepped onto the Hogwarts Express a few months ago.�

“Can the people in the memory see us?� Hermione asked, though she was sure she already knew the answer.

“No, they cannot. Not even a shadow of our presence, which is quite proper.� The light of Lupin's memory reflected off his scarred face. “Imagine how shocked I would be to see myself watching myself get on the train.�

Hermione smiled nervously. “And – and me practicing the spell on this memory won't hurt you?�

Lupin shook his head. “That is why I have chosen a rather mundane memory, and why we are practicing in the Pensieve and not in my head, which would be quite dangerous, as those who are just learning the spell tend to wipe out whole pieces of thought at a time.� Hermione looked alarmed again, but Lupin smiled kindly. “I will be neither angry nor disappointed in you if you accidentally erase this memory,� he assured her. “Now, watch what I do and follow me in,� he said, and without further comment, he leaned down until his nose was less than an inch from the thought swirling in the basin. He hesitated for a second, then submerged his head into the memory. With a silent flash of white light, he disappeared.

Hermione gasped, the afterimage of the flash creating spots in her vision. She leaned down until her nose was an inch from the swirling thought, which was no longer merely silver. Instead, the bottom of the basin had transformed into a bird's-eye view of Platform Nine and Three Quarters; the scarlet Hogwarts Express was belching steam and a large crowd of students, parents and siblings was milling about the platform.

“All right,� Hermione said, bracing herself. “One, two -� and in lieu of saying “three,� she plunged her head into the basin and fell through darkness.

She only stumbled slightly as she landed next to Lupin, who was now standing near the edge of the platform and watching himself from a few feet away. The Memory Lupin yawned widely, looking immensely careworn, and lugged his battered briefcase onto the train with him. Real Lupin followed, Hermione in tow, as Memory Lupin walked down the corridor, chose a cabin and entered. They watched as he placed his briefcase on the luggage rack, then sat down in the corner of the cabin near the window, his shabby cloak pulled up to his eyes. Within seconds, Memory Lupin was snoring lightly.

“And I think you came in soon after,� Real Lupin said, peering into the corridor. “Yes, here you are.�

Hermione watched, mouth open, as the memory versions of herself, Ron and Harry walked down the corridor and walked into the cabin, talking amongst themselves.

“If you were sleeping, how do you remember that we came into the cabin?� Hermione asked curiously.

“That's part of the magic of the Pensieve,� Lupin explained. “It brings forward an accurate replaying of events from an objective view.� Lupin tapped his lips thoughtfully with his index finger as Memory Ron, Harry and Hermione settled into their seats, then nodded decisively. “I think this is enough to be getting on with. Shall we return?� he asked Hermione, offering her his arm. She took hold of it and teacher and pupil rose up through the darkness and into the Defense Against the Dark Arts classroom. Lupin winced when they landed, though the Pensieve had set them down gently on the classroom floor.

“Now, if you will draw your wand, we will practice the charm.� Lupin waited until Hermione was ready, then waved his own wand in a lazy figure eight. “This is the motion,� he said. “The incantation is Novo Sententia!�

Hermione waved her wand and carefully stated the incantation. Nothing happened.

“Very good, very good,� Lupin said. “You will need to focus on a particular part of the memory. For instance, if you would like to modify the memory so that I do not recall taking a briefcase onto the train, you will need to concentrate very clearly on me walking onto the train without a briefcase. I believe that will be the easiest starting point. Are you ready?�

Hermione nodded and pointed her wand at the silvery substance swirling slowly in the basin. She took a deep breath, concentrated on Lupin walking onto the train without a briefcase, and waved her wand.

“Novo Sententia!� she said confidently. Almost instantly, a small, ghostly shimmer rose from the Pensieve and vanished. The substance remaining in the basin swirled very swiftly, almost angrily, as though it had been robbed of something, then settled back to its slow pace.

“Did it work?� she asked.

“I think it very well may have,� Lupin said, looking quite surprised. “Would you like to go have a look?�

“Yes, please,� Hermione said. She stepped up to the basin, then turned and looked at Lupin. “Will you follow?�

“If you like,� he replied.

Hermione nodded, then vanished into the Pensieve, Lupin following. Once more they landed on Platform Nine and Three Quarters; once more, they saw Memory Lupin a few feet away. He wasn't carrying a briefcase, but -

“You seem to have Transfigured my briefcase into a book,� Lupin said, and indeed, Memory Lupin was holding a book engraved with the letter R.J.L. as he stepped onto the train.

“Oh,� Hermione said, frowning.

“Remember, you are attempting a spell two years beyond your education, and one which some wizards never master completely,� Lupin reassured her. “It's easy enough to wipe a memory completely, but to fine-tune it takes much more skill. You have done well on your first try.�

Hermione beamed at Lupin. “Thank you, sir!�

They exited the Pensieve once again; Lupin checked his watch.

“I think we have time for one more try before your curfew,� he said. “Wand ready?� Hermione nodded and pointed her wand at the Pensieve. “Whenever you like,� he finished.

Once again, Hermione took a deep breath and waved her wand. “Novo Sententia!� She said, her eyes flashing in the light reflected from the Pensieve. As had happened the first time, a ghostly shimmer of light emerged from the basin and vanished in front of them. The remaining memory swirled angrily, then settled.

“We shall check again,� Lupin said, and they entered the memory.

This time, Lupin was carrying nothing.

“I – I did it!� Hermione said, staring in shock as the empty-handed Memory Lupin boarded the train. She beamed at her teacher. “It's gone!�

“Well done, Miss Granger!� Lupin said, smiling almost as widely as Hermione herself. “You have the eye for detail required for this charm.� They left the Pensieve and Lupin pulled the memory from the basin back into his own mind. Hermione watched, fascinated, as the basin went dark.

“Ten points for Gryffindor for such excellent concentration,� Lupin said when he had finished replacing the memory.

“Could I have one more lesson later, sir? Just – just to make sure I've got it right?� Hermione asked, fiddling with the chain of her Time Turner.

“Certainly you may,� Lupin said. “If you like, we could move on to larger items in that particular memory.�

“Such as what, sir?� Hermione asked as Lupin picked up the basin.

“Such as Mr. Potter's owl, or myself,� he explained. “Living beings tend to be more difficult than inanimate objects.�

Hermione nodded eagerly. “I would like that, Professor, thank you,� she said.

“Very well,� said Lupin, returning her smile. “But we've done plenty for now. You ought to get up to Gryffindor Tower before Filch comes this way on his rounds.�

Hermione nodded again, and with one last “thank you,� opened the Defense Against the Dark Arts classroom door and hurried into the corridor.