Harry glared at Draco, then turned to his teacher. "Perhaps you could explain to Mr. Manners here that eavesdropping is not very nice!"
"Speaking of manners," Snape calmly returned, "Perhaps you could consider that unlike you, Draco can't have visitors. Perhaps you could include him when yours come by." He neatly speared a halved Brussels sprout with his fork.
"Look, back to your cousin," Draco pressed after giving Snape a look that seemed a mix of pleading and exasperation. "Maybe too much magic will induce lifelong paranoid delusions or schizophrenic manic-depressive tendencies--"
"Stop playing psychiatrist!" Harry shouted. "I swear, you're sounding just like Hermione!"
Draco looked rather startled at that pronouncement. "Oh, well then, I will stop. Merlin forbid. My point is that it doesn't matter if your cousin loses his mind. You only need him for the warding, anyway!"
Harry slammed his knife down to the table and rounded on Snape. "You told him about the warding, too? Why don't you just shout all our plans from the ramparts? There just might be some Death Eaters who don't know the whole of them, yet!"
"Ten points from Gryffindor," Snape announced, laying aside his utensils so that he could wave his wand to enforce it. "I told you not to deride Draco's loyalties to his face."
"I'm deriding them to your face!"
"What do you want, Potter?" Draco snarled. "You want me to go under Veritaserum again and let you ask the questions this time around? Yeah, I know Severus told you about my interrogation. So, see? I'm not the only one he tells things to!"
"Since you obviously have a way to trick the serum, no, I don't want that!" Harry shouted. "And how about points from Slytherin, now? He called me Potter."
"Very well," Snape agreed, waving his wand again as he shook his head. "You two are really being extremely childish. Now, as for Harry's cousin, his sanity actually is something we ought to take under consideration--"
"Gee, thanks!"
"--because," Snape went on with a glare towards Harry, "young Mr. Dursley can't participate in any warding if he loses what little mind he ever possessed. We need him able to give consent. Harry, do you think your cousin could handle being moved here as Draco suggests if the whole process is explained to him in advance?"
"No," Harry decided. "That would just scare him worse."
"What we need, then," Snape mused, "is some sort of warding for him, but not the typical protection against attack. Warding him so that he can tolerate the presence of sorcery, so that he can see it..."
"Warding away his inherent Mugglishness," Draco put in.
"That's not even a word," Harry complained, but Draco and Snape both ignored him.
"Have you considered the Isedral Charm?"
"That only works on squibs," Snape answered.
"Sakenhaim's second principle?"
"Do you happen to have a Turkish half-vampire bound to your will, not to mention a shield of ill-repute?"
"Well, no. Hmm." Draco tapped his magically manicured fingernails against the lacquered surface of the table. "What about reciprocal magic? Harry's mother and his aunt could be the focal points."
"A Muggleborn and a Muggle," Snape sneered. "Be serious. The headmaster and I have been at this for a week. Do you think a sixth-year student is going to notice something we've overlooked?"
"You still have something against Muggleborns?" Harry challenged, a strange, taut feeling constricting his chest. He was only one generation removed from a Muggleborn, himself.
Draco rolled his eyes. "If he did, do you think he'd go on and on to me about Granger's marks in every class proving that blood isn't everything?"
"Then why are you sneering about Muggleborns?" Harry pressed, wishing that Snape would answer instead of Draco.
"I was sneering at Draco's sudden poor command of spell dynamics," Snape explained in a tone not far removed from yet another sneer. "And since I'm going to all this bother to arrange for a Muggle to come here to my private residence, I'd think you could be appreciative instead of insolent!" He turned to Draco and spoke more moderately. "Reciprocal magic was invoked by the relatives themselves, who also served as the focal points. Moreover, it requires pure blood, with a squib as the recipient, so it really doesn't apply at all."
"Those aren't requirements," Draco insisted. "Not in the sense you mean. They're just... happenstance."
Snape shook his head, though he did say, "Explain your reasoning."
"Well, the spells were only useful to pureblood families, if you think about it. Who else would have bothered with it, especially way back then?" Draco briefly turned to Harry. "This is all very archaic, hasn't been used in centuries, I think."
"I suppose it might be possible," Snape mused.
Draco drank the rest of his wine without pause, which was rather unusual. He normally sipped it quite slowly. "Well. If you really believe what you told Harry," he added in an uncomfortable tone, "then it's more than possible. Because..." he sighed, clearly reluctant, and avoided looking at Harry as he went on, "How can pure bloodedness truly be a requirement if by your own reasoning, there's actually no such thing?"
Snape looked up at that, his black eyes narrowed. "You believe that now, do you?"
Draco shrugged, and didn't meet his eyes, either. "Let's just say that for the purposes of this spell, I don't think it matters. Anyway, about the reciprocal magic," he rushed back to a less threatening topic. "All the elements are there, aren't they? Same degree of relationship bounded by... we need five opposites, but that shouldn't be too hard. Let's see... Harry's aunt was a Muggle; Dudley's aunt was a witch...." Draco began counting on his fingers and talking to himself, then said, "I only need one more. Harry, I'm sure you can come up with at least one."
"I don't even know what you're doing!" Harry objected.
"We're going to invoke reciprocal magic on your cousin, but we need one more element, so think."
Harry shoved his plate away and turned to Snape.
"It's an old spell to let family squibs temporarily see protected magic," he explained. "Think of a way in which your aunt and mothers were opposites."
"Uh..." Harry thought, but had to say, "I never really knew my mother."
"You don't have some memories from when you were little?" Draco inquired, lifting his eyebrows.
"What do you remember from when you were one year old?" Harry shot back, defensive.
"Latin lessons," Draco smugly announced.
"This isn't the time for levity," Snape rebuked him. "Do you truly remember nothing, Harry?"
Harry's voice was emotionless. "I remember her screams from the night she was killed."
Snape sat back and steepled his hands, sadly murmuring, "And you only remember that because the Dementors drew it out of you. I'm sorry, Harry."
"Yeah, me too," Harry said, his voice still flat. Then, in more suspicious tones, "Did Remus tell you that?"
"No, you did, when you rambled after your operation."
"Oh, okay."
"I can't say this isn't fascinating," Draco drawled, "but we still do need one more element to complete the star."
Harry closed his eyes, and shakily ventured, "My mother died in agony, my aunt died in her sleep?"
He felt a hand reach out to cover his, warm long fingers squeezing slightly as if in sympathy. It helped, even if the faint odor of some Potion wafted up and really put him off his food. Not that he was hungry any longer, anyway.
"It needs to be an element that involves you and your cousin," Snape quietly remarked.
Draco cleared his throat. When Harry opened his eyes, he saw the other boy staring at the way Snape was holding Harry's hand. Draco didn't comment on that, though. "Well, we'll keep working on the last element."
"We'll need a symbol, in any case," Snape pointed out. He looked expectantly towards Harry. "I believe you have something that can represent your mother?"