The Headmaster's office was lit only by a single lamp and the light of the moon coming in through the window. The rest of the castle was asleep, and a heavy silence had settled in the empty corridors and classrooms. In fact, the only part of Hogwarts School that showed any signs of life was Dumbledore's study. Albus Dumbledore himself was pacing the room, hands clasped behind his back, his brow furrowed in concentration. "You're quite sure, Severus?" he asked the only other person in the room, the sallow-faced Potions Master, Severus Snape. "You're absolutely certain of this?"

"Yes, Headmaster," Snape replied. "A Nimbus 2000 does not randomly try to unseat its rider. That was the work of Dark magic. And Quirrell was looking right at Potter, not blinking at all. We know already that Quirrell let that troll in, and that he's after the Stone, but why would he want Potter dead?"

"It suggests that he is working on behalf of someone else," Dumbledore said. "And I think we both know who would want Harry dead."

Snape didn't reply, but his right hand moved convulsively to his left forearm, where the vague outline of the Dark Mark was hidden beneath his sleeve. It hadn't been clearly visible for ten years. "Are you suggesting," Snape said slowly, "that the Dark Lord is behind this?"

Dumbledore stopped pacing and gazed fixedly at Snape, his sharp blue eyes filled with a look of understanding mixed with pity. "Yes, Severus," he said quietly. "Voldemort is governing Quirrell. How, I'm not sure, but that's not important at the moment. What's important is that Harry Potter is in danger again."

Snape didn't say anything, but Dumbledore seemed to know what was going through his mind, for he added, "Severus, I know how you feel about the boy. But if Lord Voldemort is ever going to be defeated completely, he must be kept safe. Do you understand?"

Snape nodded but didn't trust himself to speak.

"Very well, Severus," said Dumbledore, resuming his anxious pacing. "I will need to think of some way to keep the Stone safe. In the meantime, keep an extra-close watch on Harry and Quirrell for me, will you?"

"Of course, Headmaster," Snape replied in an emotionless voice before sweeping from the room, his long black robes billowing out behind him.

….

It took Dumbledore a full month to come up with a fool-proof plan to protect the Sorcerer's Stone from the grasp of Lord Voldemort, and it took even longer to get the challenges organized. To make sure Quirrell was not forewarned of any vital information, he approached each teacher separately with a request for an obstacle. Each of them (except Snape) seemed surprised but supplied the Headmaster with something that reflected their individual specialties.

But it wasn't enough, and Dumbledore knew it. While each challenge would be difficult to pass, it was still altogether possible for a competent wizard to make it all the way to the end.

"I think," he said quietly to himself, stroking Fawkes absentmindedly, "it is time that I contributed something…"

…..

Darkness had once again descended upon Hogwarts Castle. In Gryffindor Tower, Harry Potter was sleeping restlessly, dreaming of his parents, a flash of green light, and a high, cold, mirthless laughter.

But Harry Potter wasn't the only one not resting peacefully. Snape had been awoken by a vivid dream, a dream he hadn't had in quite some time but one that still troubled him deeply. He had been standing at the edge of the lake, not a day older than sixteen, his Defense Against the Dark Arts O.W.L. exam behind him. James Potter and Sirius Black had been tormenting him again, hanging him up by his ankles by use of his own spell, and Lily Evans, sweet Lily, had come to his rescue. But instead of calling her a Mudblood, as he had regretted doing for so many years, his dream self thanked Lily for her efforts. They became closer over time, got married, had a son…

…a son with untidy black hair, bright green eyes, and a lightning bolt-shaped scar on his forehead.

It was at this point that Snape would wake with a start, shaking and utterly unable to understand what the dream meant. The first part was easy enough to understand. But when Potter entered it, he got confused. What could it possibly mean?

Sleep would not return, so at length he got out of bed and dressed. Perhaps a walk around the castle would clear his mind.

The corridors were completely deserted, lit only by moonlight. Multiple times, he paused to glance out of the windows as he passed them. There was the Whomping Willow, where Potter and his gang had almost killed him. And there was the lake, where they had bullied him…

…where Lily had defended him…

Snape turned away and saw a door standing ajar. He stared at it for a moment, surprised; classroom doors were usually locked overnight by their teachers. He hesitated, then decided to investigate.

He could see at once that it was an unused classroom, but it wasn't completely vacant. There was a giant mirror on the far wall. A little curious, Snape stepped up to it before leaping back in shock, drawing his wand. There had been another person beside his reflection. But it wasn't possible…no, it couldn't be…

Snape lowered his wand slowly and approached the mirror again. Sure enough, there, standing right beside him, was Lily Evans, looking just as beautiful as she had the last time he'd seen her.

His reflection's hand took Lily's and squeezed it gently, and Lily looked up at him, smiling, her vivid green eyes sparkling. Snape moaned and reached out, his fingers brushing the glass surface, a tear sliding down his cheek, followed by two more almost immediately. Then he sank to his knees, eyes still locked on the image of the only girl he'd ever loved, and began to cry in earnest, his body shaking with wracking sobs.

"Severus," said a quiet voice from behind him.

Snape twisted around, blinking tears out of his eyes, to see Albus Dumbledore standing by the door. He looked uncharacteristically somber. He stepped forward and placed a hand on Snape's shoulder. Snape said nothing but continued to cry silently, taking deep, shuddering breaths.

"I am sorry, Severus," Dumbledore said. "I was planning to take the Mirror of Erised down to the dungeons tonight. It is essential to my plan in guarding the Stone. I did not intend for you to see it. I had a shrewd idea that you would see something…painful."

"Lily…" Snape gasped. "I…I see Lily…"

"The Mirror of Erised shows us the deepest desires of our hearts," Dumbledore said. "You, who wish that you had never turned your back on the girl you loved, see her standing happily beside you." His lips twitched a little as he added, "You and Harry have something in common, Severus."

Snape stared up at Dumbledore for a moment, unable to speak. Then he stood, wiping his eyes briskly and stowing away his wand. He was about to leave the room when he hesitated. Then he looked back and said, "Headmaster, what do you see when you look in the Mirror?"

Dumbledore gazed at Snape, a sad smile on his face. A lone tear slid from his eye and into his long, silver beard. "It seems," he said quietly, his voice shaking a little, "that you and I share something in common as well, Severus."

Snape considered asking what he meant but thought better of it. With a curt nod to Dumbledore, he left the room. He did not sleep again that night.

….

Years later, on a dark night much like the one so long ago when they had discussed Quirrell, the Sorcerer's Stone, and Lord Voldemort, Snape again found himself in Dumbledore's office, listening in stunned silence as the aged, dying Headmaster told him that Harry Potter, the only piece of Lily Evans still left, had to die in order for Voldemort to finally fall.

"I have spied for you and lied for you, put myself in mortal peril for you," Snape said angrily. "Everything was supposed to be to keep Lily Potter's son safe. Now you tell me you have been raising him like a pig for slaughter –"

"But this is touching, Severus," said Dumbledore seriously. "Have you grown to care for the boy, after all?"

"For him?" shouted Snape, raising his wand. "Expecto Patronum!"

A silver doe Patronus shot from the end of his wand, bounding across the office before soaring out the window. Dumbledore watched her fly away, and as her silvery glow faded he turned back to Snape, his eyes full of tears.

"After all this time?" he said quietly.

A lone tear slid down Snape's cheek. "Always."