Prologue: 8 Years after the end of Harry Potter and the Deathly Hallows.

It was a bright June day in Scotland, and as Hermione Weasley walked onto the Hogwarts grounds, escorted by a greying Rubeus Hagrid, she couldn't help but marvel at how different the castle looked in the summertime. The biggest change was how quiet it was—usually, the hundreds of students ensured that there was a vague rumble of conversation at all times. The lawns, too, appeared to be gradually recovering from months of abuse by hurried teenage feet.

She had visited often in the seven years since her own graduation; often enough not to be surprised at how the castle had changed since then. As the star pupil of her year, she was one of the students that teachers wanted to see again after she left—and they often had opportunities. The unusual circumstances that prevailed during Hermione's school years meant that she had come to know many of her teachers outside of the classroom, while fighting the most evil wizard of the age; others among her friends had also become teachers themselves.

This time, though, she had come on a rather unusual mission. She was, for one, alone—these days, her visits mostly involved shepherding the youngest generation of Weasleys and checking that she hadn't forgot a blanket or bottle, and coordinating affairs back at the Ministry for Magic from afar at the same time. Today, she had brought only a few empty suitcases, for she had come to help Minerva McGonagall pack up her office.

Before she knew it, Hermione found herself before a familiar and vaguely battered-looking Gargoyle. He had recovered after the last fight with Voldemort, but lost a wing. The teachers suspected that he knew where it was, but refused to tell them as punishment for ignoring his cries of pain during the fight.

"Password?" it croaked.

"Ginger newts," Hermione replied. Professor McGonagall had decided to keep Dumbledore's tradition of using sweets as passwords, but under her watch they tended more to shortbreads and biscuits than to lemon drops.

The revolving staircase was much the same as it always had been. The room at the top, though, was a mass of boxes, with silver instruments, tartan tins, Quidditch medals, and large and rather forbidding-looking books with titles such as "Performative Aspects of Modern Transformative Behaviour" and "Transfiguration: Theory and Practice." In the middle of the mess stood a rather harried-looking Minerva McGonagall, her bun—still black, but now with streaks of grey--loosened by the midday heat. She looked up and smiled warmly at Hermione.

"Oh Hermione," she said in welcome, "I do so appreciate you coming." She gave her a warm smile; even after many years of friendship, Professor McGonagall was not really the cuddly type.

"Where should I start?" offered Hermione.

"Well, maybe you'd best start emptying the shelves of that cabinet," responded the teacher, gesturing behind her desk. "That should be fairly easy to organise, if you could just try to keep the books in alphabetical order while you pack them…" Hermione nodded and walked to the cabinet. As she did so, she heard Minerva give a little sigh as she looked at the mess.

"Minerva," she said, still, as ever, feeling slightly odd at addressing her former mentor with her first name, "why don't you go take a break? I can manage the books perfectly well."

"Well, if you don't mind…" the older lady started. "I could do with a little stretch of the legs." Hermione nodded encouragingly and without further discussion, Minerva hurried out the door.

Hermione turned to the bookcase; jobs like this were well-suited to her careful and utterly organised disposition. In fact, she tended to find them rather meditative, in a way. She worked steadily for about twenty minutes, stacking the books carefully in boxes and charming the cardboard so it wouldn't break under pressure. She had finally reached the last shelf. A movement outside the window distracted her momentarily as she guided a little leather-bound book of poetry by Baudelaire with her wand, and as she glanced to her side, the book fell to the floor.

When she bent over to pick it up, cursing herself for letting it fall on her foot—even a child could have managed to at least make it fall sideways—she noticed a small Polaroid with faded colours sticking out of its pages. It was next to a poem called 'Invitation à un Voyage.' She couldn't help herself; she pulled it out to see the whole thing. It showed a woman with shoulder-length black hair and glasses sitting in a light green summer frock cut in the style of the 1960s. She was seated on a park bench, her legs tucked underneath her. In her arms was a tiny baby that waved its tiny little fists in the air; Hermione could just make out a little tuft of black hair on top of its head. The woman stroked its cheek with one hand, and occasionally looked up at the camera contently. The woman resembled McGonagall, it was true—but it could just as easily have been a sister or cousin. Why, wondered Hermione, hadn't she known of this woman before?

Then, suddenly, she became aware that she was no longer alone. She looked up and saw Minerva standing in the doorway, a look of shock on her face.

"Minerva!" she cried. "I…I…I'm so sorry, it fell out." And then, quieter, "Is it you?"

The older woman's lips were pressed tightly together; one who didn't know her might have guessed she was angry. Her face had drained of all colour. Only her eyes, glistening bright, hinted that the emotion troubling her was sadness. If Hermione had been a student, Minerva would have scolded her for snooping, but now, she realised, she couldn't use her stern demeanour as a mask; Hermione had earned the right to know her past.

She sank down onto a small leather couch in the middle of the room, breathing deeply. She wouldn't enjoy telling the story to come. "Hermione," she said, "maybe I ought to explain a few things to you. Why don't you stop packing for a moment and join me on the couch?" She conjured two butterbeers as she spoke. She thought she could probably do with their strengthening powers.

As Hermione sat down beside her, twirling her hair anxiously around her fingers, Minerva closed her eyes. She opened them, and took the picture from Hermione's fingers. Looking down at it with a pained look on her face, she opened her mouth. "That is me. Accio Pensieve!" These last two words were spoken in a stronger tone than the others, as if she was strengthening her courage.