A/N: This is my take on things. I don't believe Snape is evil, so this is for the Snape fans. :)
Dumbledore had made him do, quite possibly, the one thing he will regret for the rest of his wretched life.
The tall, tickling and yellow grass swayed lazily in the puff of air that was ruffling his heavy inky black traveling cloak. Severus gazed regretfully at the lofty white tomb, his heart hammering so loudly that it was intolerable, fists clenching and unclenching at his side.
"They've closed the school, Albus," he said unnecessarily, as if speaking with the elderly wizard again.
Of course, that was the only reason Severus had been able to get away with popping in to pay his respects. If not, he would have expected to have Potter's fists and wand thumping and cursing him into something unrecognizable before Severus was dragged off by the ministry, and spat on by every witch and wizard in society, unable to voice his justification of what he had done… though he was still unsure if killing such a man as Albus Dumbledore justifiable.
But he did not wish to elucidate the nature of his actions… particularly to the tormented boy, though he himself had taken it upon himself to wordlessly and secretly aid Potter in his hunt with every fiber of his being, and with every resource at his disposal. Severus' pride would not bother trying to excuse the regretful act of murdering the former Headmaster to him.
Not for a very long time, anyway.
He read the engravings quietly.
Albus Percival Wulfric Brian Dumbledore
1840-1997
The Greatest Wizard to Ever Live
Severus didn't need a block of stone to tell him that.
He had chosen death. Albus had given him life. It was no secret that his life had been a most horrific mess 'til after the Dark Lord's descent. Trust was not a word associated with Severus at the time; no one trusted him, he trusted no one. His life was spent as a hermit mostly, bidding his time as a muggle and praying to any faceless God that he would not be arrested.
Albus had come to fetch him one hour before his little dwelling had been swarming with Aurors. He illustrated such compassion that Severus had thought to be impossible, had sheltered him, given him employment, confided in him and gave him something he most definitely did not deserve… redemption.
"And I killed you," Severus said, softly, his tenor voice breaking.
Potter had called him a coward, though he was sure the boy didn't know at all what his killing Albus entailed unless the boy had become extremely proficient at Legilimens in a short period of time. But it had given him something to think about.
…was he?
The memory of that night was still driving him mad.
Severus was awoken to a spectacle of sorts, and he was initially convinced it was merely a very bad dream. For one (although he could not be sure, seeing as his dungeon living quarters had no windows) he did not fancy on being roused in the dead of the night by a midget with his robes on backwards. For another, it did not help matters at all that an impossibly high-pitched voice was ringing in his ears.
"Severus, Severus, we mustn't waste more time! Put on a robe, take your wand, you must come back with me and help!"
He felt a small and warm hand shaking his arm and Severus cracked open one lazy eye.
Confused, and very irritated for being so, Severus Snape rolled out of his bed, rubbing his temples in irritation and disorientation, and downed a vile vial of bright orange Rejuvenating Serum before turning his attention onto Filius Flitwick, who was hopping up and down and all over the place in a state of frenzied panic.
"What," he said sharply, having never liked the man much, "Are you going on about?"
"Death Eaters, dozens of them," Flitwick squeaked, looking hysterical and very ill indeed.
"Where were they spotted?" Severus asked sharply, his senses seeming much more acute. Sweet Merlin, surely not in the castle...
Flitwick had a crazed look on his face. "They're in the castle! Mostly by the Astronomy tower! And the Dark Mark above it! We need as much reinforcements as possible!"
His eyes widened at this, and Severus swore under his breath. Draco Malfoy had gone through with the attack much sooner than he had anticipated. True, the boy had never exactly been open about sharing his plans, although Severus had always secretly felt that Draco would be unable to follow through with what appeared to be a haphazard plan. "Filius-"
But it was no use; the diminutive professor had collapsed.
Snatching his wand off his bedside dresser, he muttered a quick spell, and he was soon dressed in his usual attire. After a second thought, he pulled on his Death Eaters cloak as well, his silver mask pocketed and a spot of brandy down his throat.
He felt a slight unrest in the pit of his stomach.
Storming out of his quarters, he soon spotted Hermione Granger and Luna Lovegood pacing in front of his office, their faces stark and gazing at him in dismay. Not bothering to question as to why they were haunting that particular corner of the dungeons, he instead swiftly snapped at them to take care of Flitwick before vanishing down the hall with a swish of his cloak.
It was not difficult to find his way to the hub of the commotion, the noise so deafening he was shocked that the entire student population had not been roused yet.
The casualties- although it was difficult to determine whether they were serious or not- were horrifying. Limp bodies positively littered the cold stone floors, and he avoided a look that Minerva gave him. He would have no time to revive the cataleptic witches and wizards.
He spotted Greyback disappear up a staircase which he was well aware led to the Astronomy Tower. Feeling as though this was unquestionably not a good thing, he side-stepped dueling Order members, Death Eaters and, to his surprise, some students, making his way to the tower.
What he saw when he reached the top of the tower was both alarming and upsetting.
"Severus…" Albus whispered hoarsely.
In his shock, Severus Snape did not catch the suggestion when Albus had spoken.
Albus Dumbledore was stooped, unarmed and weak, by the wide window of the tower.
Severus felt disgusted with himself and most definitely with Draco that the boy had managed to make it this far in his task… to corner the old man; the werewolf (Fenrir), Amycus and Alecto standing with him.
He shoved Draco roughly out of the way, making it clear that he was going to have a very lengthy and serious discussion with him, and Draco's companions, looking cowed, scurried out of the way as well.
Albus looked feeble, as though drained, and, to Severus' horror, quite ready to die.
His papery skin, weathered with age, was stark and the lines etched on his face and hands seemed to be more pronounced that usual. Remembering his place as a double-spy, Severus did his best to remove any sign of compassion from his features. Had they tortured him? Instinct told him they had not. He thought he felt a whisper of something in the back of his mind.
"Please… Severus."
Albus' clear blue eyes were penetrating his, as if willing him to understand something that Severus could not see. On instinct, he delved into Albus' mind.
And he suddenly understood what Albus was asking of him.
Albus would not suffer the cruel hands of the Death Eaters; Severus would make sure of that. Draco, who was too young, too spoiled, would not die at the incensed hands of the Dark Lord, and Severus, despite his previous understanding, would not die at the hands of the Unbreakable Vow.
Truth be told, Severus would have died when Draco failed. He had never planned on keeping the Unbreakable Vow- he had determined the instant before saying 'Yes' that this- Dumbledore's life, and Potter's safety- was something worth dying for. His usefulness was waning with the Order, and a sacrifice for Dumbledore would be his last contribution
Kill me… I will die in any case… kill me…Severus' thoughts were mixed with Albus', and he felt dizzy and most definitely sick. He, who did not deserve to be standing there, would be the downfall of the greatest wizard that had ever lived.
He knew that even if the truth of Albus' last wish were to get out among the public, few would be sympathetic.
'Death is but the next great adventure,' He remembered Albus Dumbledore telling him this. Is this how Albus wished to die?
It took him a split second to decide. He raised his wand, though he knew that what he was about to do would require him to enjoy it- to really enjoy watching the man crumple to the ground, lifeless- in order for the curse to work. So, for no particular reason, he imagined James Potter in Albus Dumbledore's stead. He contorted his facial features into one of distaste and abhorrence.
"Avada Kedavra."