There were many ways one could describe Severus Tobias Snape: git, jerk, asshole. He was once even called "the outcome of a deplorable union between a male and a female which hadn't used that sacred muggle piece of rubber" (As if Tobias Snape would allow his wife to perform magic on him).

However, if one wished to prolong his residency on planet Earth, preferably on the upper side of the lithosphere, there were two names which he had to ensure not to call Severus, whether aloud or in the mind.

Severus thought about fishing those names out of the boy's mind and let out an amused snort. Potter had a few minutes to arrive and Severus saw no point in beginning to mark yet another appallingly written essay, nor reading an additional book. Despite his notions on how to treat the brat's typical tardiness –that boy always showed up late to class! – Albus asked him to be as civil as he could, which included (as Albus empathized) ignoring any preconception he had.

His thoughts lingered on the conversation of Saturday evening. That was what led to this situation, though Severus could only blame himself.

Surely, that memory was one not to be seen by Potter. Severus attached his wand to his temporal lobe, pulling out a flimsy silver string of memories. He dropped them into the Pensieve, small characters blending and playing the events of the day before yesterday.

~flashback – two days ago~

Notwithstanding his acquaintanceship with Severus' third rule – never call him a coward or a fool – Albus Dumbledore seemed to believe Severus Snape an idiot, or at least act as if he were one.

"Albus," Severus stated coldly as he stepped into the office of the headmaster, after an intensive twelve hours bringing his ex-best friend's sister back to the world of consciousness. As much as he loathed to admit it, this set of action required the help of Weasley senior and his eldest son. Petunia Dursley, his old nemesis, had sported a few extra surprises aside from the Draught of Living Death, courtesy of the Death Eaters. Those 'gifts' required specialization in foolish wand waving, an art which Severus sneered upon.

The first unusual item which caught Severus’ eyes in the Headmaster’s office was a new pair of statues which decorated the corner. Besides the Oompa Loompa’s uniforms, which Severus courteously placed upon them in Potter’s home (house) instead of leaving them naked, the Death Eaters now sported a pair of low-quality fake beards. Nott was covered with bright neon Christmas lights in the colors of red and golden. 

The Potions Master deliberately ignored them and went straight to Albus, jabbing a parchment on his chest before letting it float down, towards the desk. 

"Care to explain the meaning of this?" He hissed. 

The skin around Albus’ mouth crinkled upwards. 

"Why, it's a note." He took the parchment with two lazy fingers, his eyes twinkling. "To one… Johnathan Prince. Oh my, seems like the author is expressing his regret regarding an incident."

"Funny, because to me it seems like the author is sitting happily on his chair and twinkling at me!" Severus lost his calm. "Stop that twinkling immediately, you meddling man! What could you possibly hope to achieve? We agreed that Johnathan Prince should stay hidden, and I'm sure as hell that if a message for him would've landed in my hands, right in front of the Weasleys, his secret would have stayed concealed! Your little hoax today almost killed me, Albus! You know what will happen if the Dark Lord would’ve find out about one of his closest servants, toying around with a muggle persona! You could Avada Kedavra me yourself, just as well! In fact, why don’t you just go ahead?!" Severus distanced his arms from his body, raising his chin towards Albus challengingly.

Though he expected it to happen, there was a sour note in his stomach as the smile disappeared from Dumbledore's face.

"Severus," Albus began, softly. He hated that tone. His arms dropped back and now hanged near his rigid body. "I gave you, at your insistence, my word that I shall never reveal the best of you." He hated Albus for bringing up the reminder of that night. "And thus, I never did nor will, Johnathan Prince included. The note which was sent to you was protected with a Fidelius. only you and Harry were able to read it. I do not take your well being lightly, as you know.

“Your secret is safe with me and will stay between those walls for the rest of my life. Although, it may not be reassuring, given that I am an old and tired man…"

Severus snorted. "As if. I will be six feet under long before."

"Don't even think about it, Severus." Dumbledore admonished, completely serious. His grandfatherly posture was gone, his back straight, mien serious. "I give you my word and my life if needed." Albus' eyes radiated with force, piercing his own, and Severus felt like he was a tiny first year again, sent to the Headmaster after charming Black's goblet to be filled only with soap.

Albus' face settled back into the familiar smile. "Certainly, in each anniversary of my death you shall bring me a pair of wool socks. It might be cold under there." Ah… there was the likable grandfather back.

Severus sighed, his tension and anger prickling from his body like a perforated balloon. He dumped himself into the guests' chair. Maybe he was an idiot, his finger light on the trigger of condemning Albus as a traitor.

"What was the note regarding, then?" He hated himself for his voice which dropped to a low tone, barely above a whisper, almost begging his mentor to give him a suitable explanation. A reason to continue to trust him, to put his mind at ease; another person to share his burden in life with.

Albus cleared his throat and wiggled on his cushioned purple seat, very much alike Potter when he broke a rule and got caught. "The so-called incident which I anticipated hadn't occurred today, due to the special circumstances which you had encountered.”

Severus’ lips tightened. “It is another plot in a long journey of trying to make me like your golden boy, then.” Of course. What was the worth of a valuable spy’s life compared to an obnoxious boy with a scar?

As if legliminizing him, Albus rounded the table and placed an assuring hand on Severus’ shoulder, giving it a little squeeze. “You need to put your faith in me, Severus. There's no need to be worried. I'm only doing what I think is best, both for Harry and you."

"That's exactly what I'm worried about," muttered Severus and the headmaster laughed.

"Now, let's talk seriously, my boy." Oh, we begin to be serious only now? "The situation will likely deteriorate very soon, due to Dolores Umbridge's wrath, which a certain Potions Master may have had a hand in causing."

Severus turned his head around and glared at him, his face carefully blank and lacking any remorse. The older man sighed, but smiled before continuing.

"Of course, as the headmaster of Hogwarts, I will take full responsibility on whatever action she carries out, while ensuring the safety of your health… and employment."

Severus raised a challenging eyebrow, wordlessly asking the Headmaster to elaborate. "I have reasons to believe that I will be forced to leave the school grounds. I must ask you to keep Harry safe. Treat him well, my boy."

"I will.” After seeing the other man's doubt, he added, with devilish grimness, "Don't worry, Albus. Despite my best efforts, I won't succeed in fulfilling the whale-sized shoes that the Dursleys have left me."

Both of the men's lips were now a thin, white line. "I am aware that Harry doesn't like staying over there, but – "

"They had locked him, Albus! Starved him. And the blood wards may be still standing, but they don't keep the Death Eaters away any longer!"

"As I began saying, Severus," two blue eyes peered over golden half-moon shaped glasses at him, "Harry showed his unwillingness to return home, but had never truly expressed to me the extent of his relatives' abusive actions. In light of the information you brought to my attention, I have no intention of letting him return there.” He exhaled. “Is your opinion of me really that low?"

The only sign of the dark-haired wizard's uneasiness was the little wrinkle between his brows.

"You never gave me the reason to believe otherwise," he answered stiffly, and saw the hurt dominating his mentor's features. "To believe that you'll do something else for an abused child."

Albus sighed again, heavily, though his voice was soft. "I'm an old man, Severus." He gazed at his palms. Abruptly, he looked all his years. "And many are the things which I regret. However, my treatment of you is one of the handful topics which I truly consider as a sin, an undoable deed. "

“I know, Albus.” He sighed with frustration. The vein in his forehead throbbed. “I… I made a mistake at blaming you. I should’ve known that you would take safety measures.”

Albus waved the crooked apology off. “Nonsense. You make a completely valid point. I am the one which owes you an apology, not vice versa. Do not - “

"Do you have any idea regarding the failure of the wards?" Severus interrupted, no longer able to let his friend wallow in sorrow nor to tolerate the pitiful tone. It was done and long forgiven, despite not forgotten. Albus gave him a curt node to show his acknowledgement of the gesture.

"Sadly, no." He uttered, thoughtfully. "Perhaps you could find something useful at your meeting."

Severus darkened his face at the notion of willingly meeting with the Boy Who Lived To Be A Thorn In His Side. "Occlumency lesson." He corrected the old man, who had the audacity to laugh.

"Why, Severus, your expression reminds me of a joke regarding you that I have heard the young Messrs. Weasley tell their brother in your absence. It goes as follows: Dumbledore and Snape walk into a bar. Dumbledore says – "

Severus' robes billowed even more violently than usual as he quickly crossed the door, dashing down the spiral staircase faster than ever.

The echo of the door slam escorted him for long, stopping only when the cool air of the Dungeons caressed his skin. Only then, Severus noticed the fundamental impact of his tirade on Albus; the old man hasn’t tried to offer him any sweets.

~end of flashback~

Severus' eyes were now closed and his head down as he tried to theorize how the Death Eaters passed the blood wards. Under his arms, in a locked drawer in this desk, rested an old book, which discussed the first known origin of the words 'blood wards'. It included a reference to a short poem, originally written in Hebrew over a yellow, crumpling papyrus.

'מים מתאיידים, אך שמך נותר

עושר הורס דם, עשיר הופך נמהר

האם דם סמיך ממים? הוויכוח בנמצא

מפריע ומטריד כל בן, בת, צאצא

על אף שכיחותו, חלק יצדדו בדם

אחרים יעדיפו את נוזל חיי האדם

אך קשר דם מבחירה הוא הסמיך מכולם

המעשייה אודות הגנותיו נלחשת בקול נעלם'

After a translating charm, Severus had no hard time memorizing the poetry piece:

'Water vaporize, thy name stays

Wealth spoils blood, rich becoming laze

Blood thicker than water? The debate goes on

Disturbing and muddling every daughter and son

Some will claim blood thickest, albeit rife

Others will favor the liquid of life

But thickest of them all, is blood by choice

The tale of blood wards whispered in a soft voice'

It appeared as if the poem hadn't given him any new information, but there was something very important that it did; it eliminated the necessity of any other parameters.

Blood and choice.

Takes one to beat one.

So, if blood and choice are both needed to establish blood wards, in order to impair their efficiency…

A knock sounded on his door, as if Potter had waited to be the maximal nuisance to his thoughts by interrupting them.

"Enter," he sighed.

Harry took a deep breath before he knocked on Snape's door.

All or nothing.

One chance to make sure he was the Half Blood Prince, before interrogating the man about every bit of knowledge he had on Harry’s mother.

He fidgeted nervously with the edge of his sleeve. Suddenly, he felt upset about not staying in the common room until Fred and George finished the joke they started telling him, a moment before Hermione reminded him about his lesson. He could’ve used something to cheer him up right now. And besides, how else would he discover what Snape and Dumbledore were up to in the bar?

Harry rapped on the black door, before his famed Gryffindor courage decided to abscond.

"Enter," he heard the emotionless order and stepped inside Snape’s office, determination resurfacing in his eyes. The dank office was cooler than the room where they studied before, and Harry wondered once again which room was it.

"Professor Snape," he greeted. Behind him, the door thwacked shut.