A/N: This was written simply because I thought the idea of Severus with multiple personality disorder (or dissociative identity disorder, as it is more correctly called) would be fun to explore. And, indeed, it was. It also became a very plausible idea, the more I thought about it. I'll save the analysis for now. Suffice it to say, I think this would explain a lot.

Disclaimer: I am not J.K. Rowling. Thus, I do not own poor Severus, and I am not making any money from this. If I did there would have been a lot more Malfoy and a lot less epilogue in that last book.


/mirror/

Sometimes, when he looked in the mirror, it seemed as if a stranger stared back at him. Yes, the features were the same, mostly. But the eyes were all wrong. They weren't his.

He had first noticed it the night his mother died. He sat beside her bed and watched as her breathing slowed—the air rattling in her lungs—and finally stopped. He had stared down at her suddenly empty body for some time, listing to the ringing silence, and when at last he looked up, he caught his reflection in the dusty mirror that hung above her dresser… and froze. Something was wrong. He watched his not-quite-twin warily as he made his way to his feet… and forgot about him entirely in the chaos that ensued. Until the next time.

By now, he had almost gotten used to it. What he hadn't gotten used to were the odd blank spots in between, when things happened that he didn't remember.

Usually, they were little things—a bottle in the trash that he didn't remember emptying, a spell he didn't recall writing scribbled in the margins of his text book, mud on his boots though he couldn't remember having left the sidewalks and stone paths… As disconcerting as they may be, these were all minor discrepancies. And so, he paid them little mind, preferring instead to brush them aside as one would an insect. Annoying, but insignificant.

Some things, however, could not be ignored.

He awoke late in the day, squinting at the feeble sunlight filtering in through dusty windows. He was on the couch, still dressed, a half-empty cup of his own specialized variety of tea on the table alongside an empty glass and a bottle of scotch—evidence that Lucius had been here.

He sat up and rubbed his eyes, trying to think past the throbbing in his head, trying to put the pieces together. But he just couldn't remember. His memory of the previous day only went so far as early evening, around 6:00, when he had heated up his frozen dinner and sat down at the little table in the kitchen to eat.

He sighed and shook his head, idly scratching at his left arm as he made his way to his feet. It seemed a bit of pain-relieving potion and nice, long bath were in order…

He made his way up the narrow, creaking stairs, stepping quickly past the first room, as he always did, even though the door was closed and locked. He slipped quietly down the hall and into the washroom where he opened the medicine cabinet and took out a small green bottle. He pulled out the stopper, took a drink, and wrinkled his nose. The stuff tasted awful. But if worked quickly, and by the time he had retrieved a fresh set of robes and started filling the tub, he was already feeling a bit better.

He had even managed to shake that strange sense of disorientation with which he had awakened. And then he started unbuttoning his shirt. His first thought as he slipped his left arm from the sleeve and glimpsed the marking there was that this must be Lucius' idea of a joke. After all, he was quite fond of hidden messages, and he did have a knack for finding interesting places to leave them…

But as he held his forearm up in the dim, yellowish light from the bulbs above the mirror, it became suddenly very clear that this was no joke. For there upon his forearm was emblazoned an unmistakable and indelible mark depicting a snake wound around and through the eye sockets and mouth of a human skull. The image itself would have been disturbing enough, given its connotations.

But what troubled him most of all was the way the snake was gently writhing, as if it were a living thing, feeding upon his flesh.

And perhaps, in a way, it was.

/mask : mirror/

Dear Severus,

After all these years, I feel that it is finally time I reveal myself. We have taken a very important step together, you and I. A step toward an existence far greater than that which we have endured thus far. We have taken a step toward greatness.

You most likely do not recall, dear Severus, but last night you and I made an oath. We stood beside our only friend and pledged our allegiance to the Dark Lord and to his cause.

We have done this, Severus, because you and I both know the truth – that there is no good in the world. There is only delusion and hypocrisy. These are truths that the Dark Lord's deeds expose. And now we shall have the pleasure of helping to educate this very stupid world.

By now you have likely discovered the Dark Mark you now bear. I know that now it seems a terribly heavy burden. Trust that it will lighten in time, as you grow accustomed to it. This is the price you must pay for the honor with which you have been bestowed.

This is very important: if you are called, you will know, and you MUST answer. Do not ignore the whispering of the mark, Severus. It holds the potential to drive you mad. And we don't want that, do we?

That being said, I do hope this letter finds you well. I trust we shall meet again soon, in the mirror.

Yours truly,

The Half-Blood Prince

/mask/

He wore the other one like a mask, covering all of his rage and malice with simple bitterness and sorrow. He let the remains of the wounded boy become his face, hiding a smirk behind a scowl. Hiding the harsh truth behind an ugly one.

Most of the time.

Now, however, he removed the mask, swept the other aside as one would move a child out of harm's way. And any who looked into those dark eyes just now would see not the pain or regret that the other one felt, but the cold, unfeeling void that lay at his core.

He had always been there when his other half needed him. He had acted as a guide and guardian, and sometimes, when it was necessary, he had been the face they presented to the world.

This was one of those times. For poor, trembling, soft-hearted Severus could never take the life of someone who had shown him such kindness, one of the only people who had ever shown him a modicum of compassion. It was unthinkable. Impossible.

And so he would do it. This was why he existed, after all – to do what Severus could not.

And so, it was he who raised his wand and recited the words that would kill Albus Dumbledore. It was he who led the group away from the castle, he who confronted the Potter boy. Later, it was he who informed a very relieved Narcissa that the deed was done and her son was, for now at least, safe.

And then, he traded one mask for another. Figurative for literal. This new mask – silver, beautifully etched in a swirling pattern that looked, to him, like the choking vines of a poisonous plant – was the one he had always longed to wear. He had been patient throughout the years of skulking and sneaking necessary to survive the predicament into which Severus, in his moment of weakness, had gotten them. He had stepped aside and let Severus take the lead, for the most part, though there were times – especially after the Potter brat had arrived – that he couldn't just stand by and watch. It had all worked out quite nicely, all things considered. They had played their role well, and now his patience had been rewarded.

Their secret was out.

No need to hide anymore. Now he could, at last, fulfill the oath he had made all those years ago. At last, he could make something of the pitiful being called Severus Snape.

Assuming Severus didn't get in the way again…

You're as much me as I am you, Severus. You're just as guilty, and you can't be redeemed. Not this time, Severus. There's no repairing a shattered soul.

Smiling to himself beneath the mask, he aimed his wand at an unidentifiable Weasley twin and fired his favorite curse. Not a killing curse like the others flying past, but a cutting curse. Not because he was merciful. Not because he wanted the boy to live. Simply because he liked it better.

This was your idea, Severus. Remember – how you longed to cut them all to shreds?

There is no redemption, Severus. No repairing a shattered soul. And yours was broken long before we killed your mother.

Wasn't it?