Snape remained where he was in a bit of a stupor until his knees instigated a painful protest. With a series of popping sounds, he shifted to one of the leather armchairs and awaited Potter's return.
"That was totally reckless, you know," snarled Potter as he fell wearliy into the opposite chair. "I don't care that it worked; it could've killed her just as easily."
Snape narrowed his eyes. "Need I remind you that you were at a loss for ideas? I had reason to believe it would work; I understand that spell far better than you do, Potter."
"That so? Which spell? Sectum or Atra?"
Snape swallowed hard against the tightening in his throat. "Both," he confessed.
Potter settled further into the chair, wordlessly Summoning the platter of party treats from the bookshelf beside the door. Snape raised his brows as it floated past; he hadn't even realized he'd set the thing down. "I think it's about time we talked," said Potter flatly.
Snape moistened his lips and drew in a deep breath. He was an Occlumens after all, and could keep his secrets if he so chose, but there seemed to be little reason anymore. "Very well. I suppose I must go first, assuming you are not too drunk to understand me."
"I never get drunk. I may act it at the occasional party, but that's just for appearances. Constant vigilance, remember?" Snape had to smirk; Alastor Moody was impossible to forget.
"Fine, then. I have no reason to lie to you, Potter. My so-called debts are paid in full. You will not want to believe that which I am about tell you, but that will be your own folly. Do you give your word to listen, or will this be a waste of my time?"
Potter rubbed his hands together, then laid them flat on the armrests. "I'll listen and hope that you aren't wasting my time."
Snape shrugged. At least that was better than nothing.
"Easier matters first, then. I believe we both know the origin of the Sectumsempra. I was never able to prove that you somehow acquired my sixth-year potions text, but that is the simplest answer, is it not?"
A hint of discomfort played across Potter's eyes before he looked away. "Not just simple, but accurate. I didn't know it was yours at the time."
"Ah, yes. All the more reason to be casting untried spells at unsuspecting people." Potter glared at him, but Snape continued. "Being Dark magic, I knew it would have more affinity for the remnants of Black Lightning than it would for the... woman. I originally devised it to break other spells, such as those that resist the Finite Incantatum. I discovered later that in the absence of magic, it would also break flesh.
"As for my knowledge of the Atra, that is a much longer tale." Snape took a slice of bruschetta from the platter and ate it slowly, deciding where to begin.
"As you well know, I served in the Dark Army during the Great War. Voldemort gave me a number of assignments, which included spying at Hogwarts and keeping him appraised of your progress. I was only too happy to inform him that you were a poor student, defiant and headstrong, perpetually one step away from being expelled in disgrace but for the fact that no one could actually catch you cheating from Miss Granger's work--and of course that Dumbledore had an unnatural affection for you." Snape stared coldly into Potter's eyes, ignoring their contempt as he pressed on. "Naturally the Dark Lord took you for an easy mark. He was repeatedly astounded by your ability to thwart him, but even upon torture, I swore to him that you were nothing special, Potter, a substandard Mudblood blessed only with incredibly good luck and Dumbledore's protections." Snape paused a moment, wondering if the message would sink in after all the years. He was pleased to see hints of shocked insight in Potter's eyes; perhaps the Golden Boy was capable of listening after all.
"But that was only one of my tasks. Voldemort's greatest foible was his impatience. He had lost ten years after your first... encounter, and he had already spent many years biding his time and 'creating opportunities.' When he finally had a strong, solid body again, he grew tired of the slow machinations of ascending to power. He wanted it to come to him easily and quickly, so that he could spend the rest of eternity enjoying it. Thus he attempted to reveal the Prophecy, and thus I was assigned to find him a weapon of incomparable power, one which would establish him as the indisputable lord of both wizards and Muggles. He ordered me to reconstruct the Atra Fulminis curse.
"Despite my protests, Voldemort also forced me to work with a partner on this project. Apparently he didn't trust me to hand over the curse like an obedient lieutenant when I was finished with it." Snape grinned fiercely. "He may have been greedy, but he was no fool. Unfortunately, that incident at the Ministry thinned out his trusted staff considerably, and I ended up saddled with the incomparable assistance of Peter Pettigrew.
"I cannot tell you, Potter, what a relief it was to place that dimwitted albatross around my neck, rather than someone intelligent like Malfoy or Dolohov. Wormtail never could find his own genitalia with the help of a cattle prod, and living alone with the Master's attentions for two years had reduced him even further. My research was cursed with one bumbling mishap after another, thanks to Wormtail and my own sleight of hand. After a year, Voldemort was practically no closer to wielding Black Lightning than he'd been on the night you humiliated him at the Ministry.
"I, on the other hand, was quite close, as was Albus. The signet ring of Salazar Slytherin contained one of the elements--it gave Voldemort the whole notion in the first place. Like all of Slytherin's secrets, this one was not intended to give itself up except to his heirs, and indeed, it cost Albus his hand, in much the same way Pendragon lost her shoulder. The ring held the keystone to Caerula Fulminis, Blue Lightning. Albus and I unlocked it and destroyed it, so that the secret to the Caerula would be lost. That left he and I as the last two sorcerers that could cast Blue Lightning, and thus the only two that could ever conceive of progressing to Black.
Snape stopped for a triangle of spanakopita. "Does Pendragon have anything to drink in this office? I'm getting parched, Potter." The younger man leapt up from his chair and found a ceramic pitcher and two tumblers in a little cabinet by the desk. He filled the pitcher from a barrel by the window; apparently Pendragon liked to drink rainwater. Odd bird, that one, mused Snape.
"Well. I need hardly point out that this was a significant responsibility. Occlumens or no, I was not infallible, and Albus was growing weaker every day. He should have let me cast the Caerula and break the signet ring, the arrogant prat. He had never used Dark magic before, and to start with a Lightning curse... it was not worth the price." Snape stopped as his voice grew thick, and took a long draught of water. Potter remained at rapt attention, his eyes as round as saucers.
"Eventually Voldemort recognized that Albus had been wounded by Blue Lightning. My sabotage was nearly revealed, and Albus was forced to lie--to claim that he'd stolen the Signet Ring from me and unlocked the Caerula on his own. He and Voldemort had a powerful confrontation during your sixth year--of which you and the rest of the wizarding world remained blissfully unaware. Albus weakened the Dark Lord enough to slip into his mind undetected and steal the location of another Horcrux, but we both know that was all folly. The Horcrux in the cave had already been destroyed and Albus took that Dark potion for naught.
"That was why we agreed to end our pact that night, Potter. Our pact. We were the last paladins of the Caerula and we agreed to take it to the grave together. Albus was succumbing to Darkness--he called to me that night through my Mark! He knew Draco Malfoy was coming for him, knew that the boy was driven to spare his family. When the stupid child couldn't kill him, Albus tried to provoke his pride and the damnable prat went and caved in! Arrogant and defiant for sixteen straight years, and on the one night it mattered, the Malfoy scion developed a conscience. Fate sometimes deals the strangest hands.
"I was supposed to join the raiders and provoke my way into a fight to the death. Voldemort would perceive that I had served him faithfully to the end, and would appoint someone to continue my research. I had a whole series of false clues prepared for my successor. Obviously I ended up having to improvise and... take care of Albus, but that still worked nicely within the plan. You see, Albus and I both believed you would kill me, Potter; we had rather counted on it. I was to be a practice run for you, the whetstone upon which you honed your skill as a murderer before facing the Dark Lord. And as always, you were too distracted by the unfairness of your life's circumstances to concentrate. Damned fool! Between you and Malfoy, the two of you nearly cost us the war that night, fighting ineptly for opposite sides. What a farce!" He paused again for another draught, enjoying Potter's indignant expression as long as possible.
"To this day, I don't know why I ran. Force of habit, I suppose--always keeping up appearances for Lord Voldemort. Once I Disapparated at the rendezvous point, I realized my mistake. I had no more pretense for my slow progress on the Atra. Voldemort himself would supervise my research, and he would not fall for the subversive tactics that befuddled Pettigrew. I was supposed to die with Albus, not return to the Dark Lord like the Prodigal Son with the knowledge I had! Yet I was a coward, Potter. I couldn't bear to take my own life. I was betrayed by hope, by the belief that once again, I could fabricate my way through this disaster and live to see another sunrise."
Snape sighed deeply and stared at the fire for a moment. "I suppose that was precisely what happened. I had certainly 'proven' my loyalty, so Voldemort permitted me to survive in Azkaban. He undoubtedly expected to destroy the prison at some point and set me back to my task, but you managed to put an end to him, didn't you? Which was lucky for both of us, I suppose, though I questioned that every day for the past fifty years."
"Mother of Merlin," said Potter in a scraped voice.
"Spare me the sentimentality and don't interrupt, Potter. I'm just now getting to the part that matters. You see, I made a serious mistake, Potter. I underestimated Peter Pettigrew. I didn't think he could possibly comprehend the research I'd done, much less continue it. After all, the Blue was lost to all but myself--even if he could get that far, the critical prerequisite for the Black was missing."
Potter shook his head. "So how did he get past it?"
Snape closed his eyes in a pained grimace. "I learned something about myself in Azkaban, Potter, something I never even suspected."
Potter raised his hands with an expectant shrug.
"I talk in my sleep."
Potter gaped, then rolled his eyes and dropped his face into his hands. Snape reached irritably for a slice of orange but only held it in his hand and scowled.
"The price of too much Occlumency, I suppose," he finally grumbled. "When the other inmates complained, I quickly learned to suppress it, but it never even dawned on me that I'd done it in front of Pettigrew. He was such a perpetual whiner, I unthinkingly assumed that if I'd ever woken him up, he would have spent the next day making me painfully aware of the transgression. Wormtail spent one summer holiday in my old home with me, you see, which was precisely when we destroyed the Signet Ring. Apparently the little bastard was cunning enough to recognize an opportunity, and managed to glean the proper incantation from my mutterings." Snape sighed bitterly, gritting his teeth.
"It's a wandless spell, Potter; that's why it destroyed Dumbledore's hand. His very flesh rebelled against channeling that Dark energy. I could have done it without so much as a singed fingernail." Potter gaped again as Snape raised the heel of his hand to his eye and impatiently brushed away a tear. "Sodding sneaky bastard gave me that bloody jolly grin of his and immobilized me. I was stuck there watching the whole ordeal, damn him to seven hells."
"I know how that goes," agreed Potter glumly. He held out his tumbler. Snape smirked humorlessly and clinked the rim of his own to Potter's in a grim toast. Potter froze with the tumbler halfway to his lips, however, and stared at Snape so intensely that the older wizard frowned and checked over his shoulder for some unknown mischief behind him.
"Someone step over your grave, Potter?"
"If... If the Lightning spells are wandless, then you..."
"Could have walked out of Azkaban at any time in the last half century. Yes, Potter. I'm impressed that you caught on so quickly; that couldn't have taken more than sixty seconds."
Potter shook his head. "Why?" he croaked.
In a rare display, Snape dropped his guarded expression and trademark sneer, gazing at Potter in sorrowful resignation. "What options did I have, Potter? I could cast the curse and walk away, and spend a lifetime being pursued by Aurors seeking to kill me, and by would-be tyrants seeking to torture the secret from me. I was never wealthy, but all I had was seized by the Ministry upon my conviction. How far could I run with no means, no wand, nothing but the clothes on my back? I believe your aunt and uncle impressed upon you that hunger is a powerful motivator, did they not? If I left those walls with no magic at my command but the Caerula Fulminis, I would end up forging a trail of blood for tea and biscuits. I have no taste for senseless murder, Potter. I never did." His upper lip curled in disgust, and the rest of his face quickly recognized the engram and followed suit.
"But why did you never tell anyone? Fifty years, Professor Snape!" Potter looked as though he might shed a tear as well, and Snape regarded him with cold disgust.
"If the Dark Lord thought that I'd betrayed him, not even the walls of Azkaban were thick enough to keep him from me, Potter. Particularly if I was his only hope to find Black Lightning. While he lived, I dared not speak the truth. And after that... well, you tell me, Potter, would you have believed me? I think not. You would believe I made it all up in a pathetic attempt to escape the sentence I so richly deserved, hmm?
"Even now, there is a hint of doubt in your mind. By morning, you will have questions and counterarguments. If you are feeling charitable, you will pose them to me, and I will have the dubious pleasure of baring my soul all over again. If not, you will consult your colleagues, who will listen to the summary of my tale with bulging eyes and red faces, and remind you, correctly, that I am a liar. Every word you utter in my defense will make them click their tongues condescendingly as they take you for a gullible fool, at which point you will either stop defending me or stop believing."
Potter's jaw clenched. "Well, you have me all sussed out, don't you? I don't suppose--"
"I told you not to interrupt," Snape barked over him, shifting in his chair. "We've almost made it to the end. Thus: my own dreams betrayed my secrets to Pettigrew, and he had all the notes I kept for Voldemort--the false and the true. It apparently took him nearly forty years to decrypt them and complete the forensics, although perhaps he was incarcerated for part of it; I neither know nor care. I'm pleased to hear that he was too weak to contain the spell, although I wish Miss Pendragon had not been in the way when he made the attempt."
"It's not Miss Pendragon," Potter noted quietly. "It's just Pendragon."