Chapter 1: The Replacement

"Always."

The silver mist of the doe patronus faded and a lone tear wound its way between the crinkles on Headmaster Dumbledore's cheek.

Severus Snape lowered his wand, bereft of the bittersweet magic that was his memory of Lily Evans. He watched as the aged wizard in front of him sunk into the throne-like chair behind the headmaster's desk. For a while, the only sound in the room was of Fawkes' preening and the wet March sleet that hit the lead glass window, brought there by the westerly gale that was typical for Scotland. The students had long since gone to bed.

At length, the Headmaster spoke. "I have done a significant amount of research lately." He laced his fingers together on the desk, creating a pattern of alternating healthy pink and shrivelled black. "Into several important matters."

Severus took a seat in the smaller chair facing him, and gathered his cape around his body. Lately, the Headmaster had grown distant and thoughtful, and their conversations more often than not pertained to matters of war and death, and lasted long into the wee hours. Today was no exception, and Severus' was still reeling from the revelation that Harry Potter was a boy marked for death.

"As it appears," said Dumbledore, "there might be a different solution to this travesty, one I hope will be better, in the end."

"Really?" Severus leaned forward. He did not have much hope, but where the Headmaster went, he would follow.

"Severus, when you took the unbreakable vow with Narcissa, you inadvertently led us to a path that hastens my own demise. This, as you know, thwarts my original plan and I've been looking for alternatives."

Severus dipped his head, prompting the Headmaster to hum gently. "Rest assured," he said with the brevity of someone who has long since stopped regarding himself as anything but a means to a cause. "I do not blame you. You did what you could, acting on demands I myself placed you under."

Severus nodded jerkily. There was a slight pause where he couldn't quite look Dumbledore in the eye.

"Now, the –ah– solution I have found," said the Headmaster, "might not only spare my own life for a while, but also Harry's, and perhaps also your soul, and Draco's." Cautiously, he continued, "it involves you greatly, and as I fear for your reaction, I must ask that you hear me out until the end. Severus, are you listening?"

"Yes, Headmaster." Severus drew his eyes up from the worn hardwood floor. Dumbledore's sharp blue eyes met his own and he braced himself.

"There is a spell," said Dumbledore. "An age-old spell. It has been used and misused throughout history, but was created before we separated magic into light and dark. Even Tom Riddle merely scratched the surface of it when he made that mark on your arm and had he known its true potential, the world would already have been a terrible place." He pointed at Severus' forearm. "The spell ties two souls together with a strength that surpasses any other magic known to man. Severus, you are a very clever man. Can you guess of what I speak?"

Severus frowned, chasing memories of unwholesome texts read in the dark, long ago. "I cannot say I know of such a spell," he said. "You mentioned soul-magic?"

"Not exactly." Dumbledore stroked a hand over his beard. "But this spell is strong enough to overrule your bond to Voldemort–" he paused as Severus flinched. "It will also allow you to break your pledge to Narcissa."

"I take it you intend to cast this spell on me then. May I ask what it entails?"

The Headmaster's gaze strayed to the window. Outside, the sleet had turned to hail. "If you do this, you can aid Harry in his task to kill Tom. There is something I have not told you, you see. A suspicion I have about the way that he has protected himself. But unless you agree to be bound by this spell, I cannot –I dare not– reveal its nature."

Severus' neck prickled. "Bound?"

"Yes. There are risks of course, there always is. To save Draco, you must take the blame when he fails in his mission. But that will be the easy part. In the end…" Dumbledore watched him keenly. "In the end it might allow you to take Harry's place as Voldemort's dispatcher."

Severus was not braver or more valiant than the next man; the ice that went down his spine momentarily claimed his breath. Dumbledore sighed.

"Dear boy, I would not ask this of you had you not made it your life's mission to protect him. You said once that you would do anything and so I drive you as far as I can." He paused. "Have I finally reached your limit?"

Severus knew that he would have to pay for his mistakes in the end. Ever since Dumbledore had asked him to return to the Dark Lord's side, he had known that his life was forfeit. He had grown accustomed to the thought. But having to face the Dark Lord, one-on-one and all alone…that responsibility was terrifying.

"Tell me more of this spell," he croaked.

"First I must warn you." Dumbledore said. "For this to work as planned, we must act so that Tom believes that I defeated both yourself and Draco. When you face him then, there is the risk that he will kill you both directly. It is imperative that you maintain your rank and his regard."

Severus shrugged a shoulder. "I already have his favour," he murmured. "As his obsession with Potter grows, he relies on my advice."

"I am aware of that." Dumbledore nodded. "The spell might even aid you in occluding against him, although I cannot be certain of that. Nevertheless, if you do this, it buys me a little more time to help Harry and it allows you to aid us as well. Perhaps that will be enough."

"And in the end, I let the Dark Lord kill me in Potter's stead?"

"Precisely." Dumbledore sat back. "You and I will sacrifice our lives to save the young ones. That is not so terrible, is it?"

"The spell, Headmaster?"

"Yes. The spell." The old man rubbed a shrivelled, black hand over his brow. "The spell, Severus is that of slavery."

The Headmaster might as well have punched him. "You wish to bind me?" He shook his head, slowly, knew he couldn't quite conceal the hurt. "Do you feel that I am somehow lacking in my duties to you?"

The Headmaster smiled. "I think you perform them admirably," he said. "I could not ask for more. Casting the spell between the two of us would make no sense." He made a grimace, as though wary of Severus' response. "It has to be Harry," he said quietly, "Severus, you understand? Only then can you replace him in the final standoff against Voldemort."

Severus did not flinch this time. He was too busy controlling the horror that threatened to turn into rage. "Not so terrible indeed," he bit out. "Potter. Out of all people, you wish to tie me to the child of my enemy? Forget it, Dumbledore. You are asking too much."

"Yet every action you have partaken these last few years has been for him," stated Dumbledore calmly. "And if not for him, then for Lily." As an afterthought he added "And for myself. Will it really make such a large difference? "

"You really think he won't take advantage?" Severus barely noticed that he was now looming over the Headmaster, fisting his hands on the coarse desk. "He will rejoice in this opportunity," he hissed. "He will make me do his bidding. Out of all your ideas, Headmaster, this is by far the most dangerous. You cannot believe for a second that he won't make me obey every juvenile, impulsive thought that enters his dim-witted skull?"

Dumbledore sighed. "If you do this," he said gently, "I will take care of Harry. Severus, you have my word of that. You need only see him in class. The boy has a good heart. He will understand, and treat you with respect. I will make sure of this. In time, when the end grows near, he will have learned to appreciate your sacrifice."

Restlessly, Severus walked over to the window. But the night was dark, and all he could see was his own haggard reflection. He felt Dumbledore's eyes on his back.

"What of the Dark Lord?"

The Headmaster swallowed. "Tom cannot know," he said. "That is crucial. But the spell should see to that. My hope is that this bond will aid you and strengthen your ability to occlude. If it does, you can continue spying on him, which gives us a significant advantage. It means that I can reveal to you what I suspect about Tom's defences so that you can gather the necessary information to destroy them."

'Them', he said. What did that mean? There was silence in the oval office for the longest time. The hailstorm had lessened and Fawkes slept atop his perch, head tucked beneath a red-and-golden wing. At last, Severus cleared his voice.

"If this is truly your wish, Headmaster, then promise me to keep Potter at bay. Keep him away from me. I cannot promise that I will be able to control myself."

Dumbledore inclined his head. "You have my word."

"And do not tell him why."

"I will not. But you cannot deny him if he asks."

Dumbledore stood from his desk, and walked to a cabinet beside the fireplace. He poured two drinks, and joined Severus by the window.

"Here," he said, a slight catch in his voice. "I daresay we need it." He put an ageing hand on the stone ledge, upsetting the dust that coated it and gave Severus a sidelong glance. "Time is of the essence now. We must act before Draco consummates whichever plan he has forged."

Severus could barely feel the firewhiskey going down; he was already numb. "Very well, Headmaster."

"I will see you tomorrow then, after dinner. We shall explain to Harry and I will help you cast the spell."

For a second, Dumbledore looked as though he was about to touch Severus' shoulder, but he withdrew his hand at the last moment and went over to the bookshelf. "Take this with you," he said, pulling out a leather bound manuscript. "It has details on this bond that you will need to study. Come prepared tomorrow and we might avoid some discomfort on your part."

"As you say." Severus accepted the book and put his empty glass on the mantle.

"I would wish you a pleasant evening," said Dumbledore said quietly, "but I fear for your reaction. Severus, I hope you know I'm not taking this lightly. If I could see a better option, I would choose that in a heartbeat."

Severus gave the Headmaster a nod of acceptance, which surely looked more valiant than he felt. The only bright spot he could see was that at least he wouldn't have to kill the old man, as was the original plan.

He had said 'anything', and anything was what he would do. But the book lay heavy in his hands.

~o~

He had Defence with Potter the very next day.

Apparently, the world did not stop moving just because Severus Snape stood on the edge of a precipice. That night, he had not slept, but read, and paced his room, and then read some more. Only to find that yes, the book confirmed the Headmaster's idea, regardless of what he might want.

He was so tense he could not eat at all.

It was once thing to sacrifice one's life in open battle, but this? What would happen if the curse claimed the Headmaster's life? Once forged, the slave-bond could not be broken. Potter would be resentful, surely. But how would he seek revenge?

Ten o'clock came around all too soon. And true to form, Potter sauntered into the classroom barely on time. He must have noticed him watching, because he sent Severus a mistrustful glare. To think that this foolhardy teenager was his master-to-be? Damn the boy and those terrible eyes. Anyone else would have been better.

Potter looked so clueless that he wanted to get up and shake some sense into him, but he knew he could not slip. He did not wish to disappoint the Headmaster.

"Before we start, I want your dementor essays," he said, summoning the scrolls. "And I hope for your sake they are better than the tripe I had to endure on resisting the Imperius Curse. Now if you will all open your books on page –what is it, Mr. Finnigan?"

Severus answered questions about an article in the Prophet on inferi, hinting quite heavily that it was all nonsense and that the episode had really been about a certain 'Order member'. As he walked the isle between desks, he overheard Potter whispering to Granger and Weasley.

"I thought Snape and Mundungus were on the same side? Shouldn't he be upset he's been arrested?"

"Quiet, Harry," hissed Granger, in an even louder voice than Potter had used. Severus felt his hackles rise.

"Miss Granger," he said, making her jump in her chair. "Clearly your endless wisdom cannot be contained. Ten points from Gryffindor." A few of the Slytherins laughed. Severus motioned to an area in the corner, which he had cleared of desks. "Step forward, Granger. You might as well demonstrate your knowledge."

Hesitantly, she did what he asked. Severus took a moment to deliberate what would upset Potter the most.

"Longbottom. Join her." It was an uneven match and Severus took warped pleasure in watching the dread on Longbottom's face as he made his way forward on shaky legs.

"I would have you practice on Weasley, Granger, but the boy is apparently so dense he can't even apparate half an inch across a room. I fear for his safety."

Weasley's face was now a shade redder than Longbottom's. Granger seemed angry, yet determined. But the look on Potter's face was by far the most satisfying.

"Non-verbal spells only, Longbottom," said Severus lazily. "You may begin."

Granger allowed Longbottom the first move. He fired a bat-bogey hex, which she repelled easily using the counter curse. Granger then flicked back a langlock. Severus recognised it by the light blue sparks that bounced off Longbottom's shield charm. Where on Earth had she learned that?

"Move, Longbottom. It looks like someone drenched you in syrup. She isn't even trying."

Longbottom glanced at him, then took and uncertain step towards Granger. "Expelliarmus," he cried, too flustered to remember not to speak the incantation. Granger just grasped her wand a little tighter and the spell bounced off.

"That was tame," said Severus, making Crabbe and Goyle snicker. "From now on, I will penalise whichever one of you takes too long to retaliate. A stinging hex shouldn't be too painful."

Severus met Potter's eyes across the room. He looked mutinous now, and for a split second, Severus wondered if what he was doing was wise. But it did not last long. In just a few hours, this power he had would be gone, and Potter would be the one tormenting him. It was best to enjoy it while it lasted.

"Granger, proceed." He flicked his wand and a small, red spark hit Longbottom's hand.

"Hey!"

The whole class froze. Severus turned to see Potter stride forward, wand raised and somehow, the tight knot in his chest eased its hold. Good. This was exactly what he needed.

"Why don't you demonstrate yourself, if you're so great at it?"

Severus smirked. "Why Potter," he said silkily, "that sounds almost like a challenge."

It was, judging by the steel in Potter's eyes. "You don't get to torment them," he said. "I've had enough of this. I'm taking over for Neville."

Oh, grand old Gryffindor chivalry. Severus sneered. "Very well, Potter. If you're quite sure you're…up for it?"

"Definitely," snarled Potter, taking Granger's place. "Unless you're afraid a student will get the best of you. Professor."

Severus waved Longbottom away. "Non-harmful spells only, Potter. Until one of us is hit or disarmed."

Potter nodded, jaw clenched.

"On my count, then. One–two–"

Viper-quick, Severus struck with a disarming spell. But unlike in their disastrous occlumency lessons, Potter was well prepared this time. He ducked, and retaliated quickly with stupefy.

Potter had apparently been practicing his wand work. Had he felt the least bit generous, the quick reflexes might have impressed him. The boy managed to fire three rapid curses in a row, launching the two last ones nonverbally.

"Blocked again, Potter. Your every move is written there, on your face. It makes it only too easy to–"

They had drawn close to one another, and Severus suddenly cast a stinging hex, which would have hit Potter squarely in the face, had he not responded with astounding swiftness. The shouted protego was explosive, and Severus fell back, bruising his hip on a nearby desk.

For a moment, Potter looked just as startled as he was, but he recovered quickly. "Stupefy," he cried. "Reducto."

"Harmless spells only," Severus hissed. "Are you incapable of following simple instruction?"

But then–

"Levicorpus!"

That was when Severus got angry for real. That spell–Potter must have learned it in the pensieve. By watching his father do the very same to him.

"Deprimo. Impedimenta." A gale cursed through the classroom, throwing Potter off balance. The tripping jinx knocked him off his feet.

Severus wasted no time in casting the disarming spell, but in his rush to win, the magic he used was so strong that it threw the boy backwards.

Potter's head hit the wall with a dull thump and Severus' heart stopped dead in his chest.