Author's Note: Unbetaed. Complete. Another case of 'I must get this out of my head so I can sleep'. A Pensieve would be really useful sometimes...

Finally learning more about Snape and his motiviations in DH has opened up a whole world of possibilities to me for missing scenes and fill-in-the-blanks fics set all through the whole series. This is the first one. I'm sure there will be more. Not really any DH spoilers in this one…

What Might Have Been

Patrolling the corridors of Hogwarts late at night did have its benefits. Catching pairs of wayward seventh-years holed up in niches, deducting House points from fifth-years hurrying back from the library far too long after curfew, aiming a sharp kick at Filch's cat when it insisted upon prowling a few paces behind him.

Much later at night, when even the most rebellious students were tucked up safely in their dormitories, patrolling the castle rewarded Severus Snape with a different kind of contentment.

Silence.

A chance to clear his head and gather his thoughts.

He needed that time more than ever this year, now that Harry Potter had come to Hogwarts.

The boy was a spitting image of his father, and Severus had instantly latched on to that as an excuse to hate the boy every bit as much as James.

But those eyes… those startling green eyes… He had heard years ago the boy had inherited that feature from his mother, but never could he have imagined them to be so, so alike. Could there be a crueler juxtaposition of hatred and love than those brilliant orbs staring from the face of James Potter reborn?

It was torture.

Memories of her had been assailing him since that first Potions class with the boy. Thoughts of his childhood friend invaded his waking hours, and images of her walked through his dreams until he feared to close his eyes, knowing the sweet torture sleep would bring.

His lack of sleep was making him harsher than usual towards his students and other teachers alike. He kept to himself, avoiding the staff room and the Great Hall whenever possible. He wasn't nasty for the sake of it, but his temper was close to breaking point.

Albus, of course, had sensed something was amiss with his Potions teacher, and Severus didn't doubt the perceptive old man knew exactly what the problem was. The headmaster was the only person who knew everything that had happened between Severus and Lily in their younger years, and the fatal mistake that had led to her death.

They'd had a handful of conversations over the summer about the Potter boy's return to the wizarding world, but Severus doubted Albus had suspected how profoundly the event would affect him.

Turning the corner into a disused corridor, Severus wiped a hand across his weary eyes and stared at the floor. The fine layer of dust on the smooth stones beneath his feet had been disturbed; a trail of footprints wound its way along the corridor towards a distant door. Severus followed, wand out to light the way.

The footprints were small… a young student, no doubt. There would be serious consequences for one so young being out so late at night.

Reaching the door where the footprints led, Severus noted there were no similar footprints leading away from the door again. Caught, he thought with grim satisfaction. Without hesitation, he flung the door open, his wand sending out brilliant balls of light to illuminate every corner of the room.

The empty room.

Frowning, Severus took a step forwards, allowing the door to close quietly behind him. He cast a revealing charm, but to no avail; he was alone.

As he turned to leave, though, something caught his eye in the far corner of the room… a towering object covered with a deep blue cloth.

Curiosity piqued, he walked towards it. Hogwarts was filled with all sorts of strange objects, but Severus had been in this room countless times and had never noticed this one before.

Lifting the edge of the blue cloth cautiously, his wandlight illuminated an ornate, gold frame. Lifting it further, he discovered the frame contained a mirror. A quick yank caused the cloth to tumble to the floor before him, almost burying his feet.

The towering mirror reflected nothing of the room in which he stood. The strange writing that arched across the topmost edge of the frame looked like gibberish… but upon reading it backwards, Severus suddenly realised what he had stumbled upon.

He drew a sharp breath and stepped back.

The Mirror of Erised.

He'd heard tales of the mirror occasionally in the past, but never had he imagined it resided at Hogwarts, nor that he would stumble upon it.

Did he dare?

The surge of longing that swept through him at the thought of seeing her was too powerful to resist, and he moved a step to his right to stand directly in front of the mirror.

For a moment, nothing happened.

Then he saw his own reflection… but wait, no, it wasn't the man who stood before the mirror. They were identical, yet different in the subtlest ways. The man in the mirror was dressed in a simple shirt and trousers, not the formal teaching robes Severus wore; his face was smoother, not lined with worry beyond his years. And he was smiling.

Out of the mist beyond the man in the mirror, a woman walked forwards, and Severus' breath caught in his throat. Red hair cascading over her shoulders, Lily wrapped her arms around mirror-Severus from behind, standing on tip-toes to rest her chin on his shoulder. He glanced sideways at her and said something, and she laughed, her brilliant green eyes lighting up with happiness and love.

Without knowing he was moving, the real Severus reached his hand out towards her, only to find the cold, unyielding surface of the mirror separating them. Such an intense feeling of loneliness overwhelmed Severus at that moment that his knees gave way, and he sank to the ground, his outstretched hand sliding down the mirror that was showing him not only what he so desperately desired, but what might have been, had different choices been made.

Glancing up at the couple in the mirror again, he saw them both turn as another figure ran into the scene. As mirror-Severus bent down and scooped a young boy into his arms, the real Severus let out a gasping sob of despair and buried his face in his hands.

His shoulders shook as he fought to control the roiling sea of emotions he had managed to conceal for nigh on ten years. Lily was all he had ever wanted, but to see the family… the child… his child… how could he have wanted something so desperately and never even realised until this moment?

With a deep, shaky breath, he dared to look upon the perfect scene again. Mirror-Severus had one arm around Lily, and he leant over and kissed her tenderly on the cheek. The boy, standing in front of them now, was about six or seven, with Severus' straight, black hair and those same, startling eyes as his mother.

Potter's eyes, Severus realised with a start.

How could he ever look at the boy again without remembering this… without remembering another boy who would never exist?

"It is a bittersweet thing, seeing your heart's desire only to know it can never be real."

Startled, Severus sprang to his feet and turned towards the voice of Albus Dumbledore. The headmaster was watching him with a mild expression, standing a few paces away; Severus had no idea how long the other man had been there.

"Albus, I–"

"It's quite all right," the other man said, forestalling Severus' attempt at apology. "You're not the first to stumble across the Mirror of Erised, nor chance a glimpse into its depths."

The headmaster paused… then, "Did you see her?"

Severus nodded silently.

"And what else?" the other wizard prompted.

"A… a boy," he said with difficulty. The lump in his throat was growing again, and he fought the desire to turn his eyes upon the mirror once more.

Sadness tinged the headmaster's tone as he murmured, "Ah, I see."

"It was foolish of me to come here," Severus said, attempting to redirect the conversation. "I was following footprints in the corridor; I thought a student might have been out of bounds."

"I daresay that would have been our young Mr Potter," the headmaster said with a nod. At Severus' look of confusion, he added, "I discovered him here earlier tonight, much the same as I have just come upon you. I impressed upon him the dangers of the mirror, and of dwelling on the past. Curiously, your vision and his own had something in common."

Lily.

Severus considered what Potter would have seen, and his lip curled at the thought of James being part of that vision.

"Sadly, neither of your visions can ever be," the headmaster continued. "I hope you realise that and do not linger on what might have been."

"Of course I realise that!" he said sharply. "She's dead! Is it wrong of me to wish it weren't so?"

Dumbledore shook his head, unfazed by Severus sudden burst of temper.

"No, Severus, it's not wrong to wish things were different," he said calmly. "But take care; many a wise man has wasted away in front of the Mirror of Erised, too entranced by his desires to face the harshness of reality. The mirror will be moved tonight and I beg you not to go searching for it again…" The headmaster paused for a long moment. "Perhaps it would be better if you didn't recall what you have seen at all?"

"No." Severus backed away from the other man, his voice carrying a pleading edge when he spoke again. "You have my word that I won't search for the mirror again, Albus. But please do not take from me what I have seen… it's all I have of her. Please."

The headmaster considered Severus' plea in silence, and then finally nodded.

"Go, then," he said. "I must move this before dawn."

Severus turned silently headed towards the door. As he reached for the handle, the headmaster spoke again.

"Bury your feelings deeply, Severus. Should he return as we have feared, more lives than we can count will depend on your ability to conceal all."

Severus glanced back at the headmaster, who was covering the mirror with its billowing, blue cloth again. The surface of the mirror was blank now, showing only a greyish mist. He knew by the morning it would be gone from the room, perhaps even from the castle.

And though he would never see it again, the memory of what he had seen in its depths would stay with him forever, concealed within the deepest, most private recesses of his mind.