Harry sat and contemplated this for a while, avoiding eye contact with the other two. How had his experience as a Gryffindor been so very different from that of the other Harry?

"Do you think," he eventually managed to say, his voice slightly tremulous, "that Professor McGonagall knows?"

Snape's voice was quiet. "She will likely suspect. I remember her trying her best to convince the headmaster to leave you with a different family. 'The worst kind of muggles imaginable,' she called them, when they returned from dropping you off after that Halloween. The Albus of this world certainly was not surprised when I came to him with Harry's testimony, but he viewed it as a necessary evil for the sake of the blood wards. It took my threatening to alert the ministry, as per my legal obligations and the requirements of my unbreakable vow, to get him to agree to the compromise we eventually reached."

Harry thought about this. He supposed it made sense, but some things still didn't add up for him. "Why take him at all?" asked Harry. "You mentioned monitoring wards, wouldn't they have been enough? You didn't need to take him home for him to be safe."

"Albus made that point, too," nodded Snape. "However, I made a vow to protect Harry Potter, and that meant not leaving him in a place in which he was unwanted and scorned by his own family for two months every year." He paused, seeming to choose his next words carefully. "Without going into too much detail, my upbringing shared some commonalities with that of Harry, so I know the realities of the situation. I could not be a party to allowing the same harm to come to a child in my care, especially one I had sworn to protect. Not if I had the power to prevent it, at any rate."

Harry nodded glumly, feeling thoroughly let down by his own head of house. It left a hollow feeling in his stomach, and he found that he didn't want to continue this line of discussion, so, when he felt better able to speak, he changed the subject to a less personal one he wanted to address.

"How come Voldemort didn't return in your world? "he asked, just as the silence threatened to become awkward.

Harry's alter-ego hesitated at this, glancing at Snape, whose brow furrowed the tiniest amount, giving the appearance, as far as Snape went, at least, of deep concern.

At length, Alium-Harry began to speak, hesitantly. "OK, so, please don't blame yourself for this." he said, his voice slow and careful, his eyes on Harry's face. "You couldn't have known because no one bothered to tell you."

Harry frowned at this, feeling a sense of unease, but nodded regardless. His alter-self continued. "You mentioned the Mirror of Erised, in your first year? Well, our Dumbledore had a plan, you see. He set up the trap to lure the Dark Lord, with enough layers that it'd take a while to figure out, so the possession would gradually weaken Quirrell. When he was weak enough, the last of the protections was revealed, and Quirrelmort went to get the stone. Quirrel wasted away in front of the mirror (his life-force was sapped by it and his body was on its last legs anyway) and the Dark Lord's spirit was trapped by the mirror. It's been there since; the mirror makes a nice little fantasy world for its occupants. I doubt he wants to leave. So, the upshot is that in my world, he never came back."

Harry felt like he'd jumped into a cold lake. The realisation hit him— if they'd not gone after the stone, if they'd just listened, if they'd just trusted, Voldemort couldn't have come back. It was all Harry's fault. Snape had been right all along— he was arrogant.

"No," he breathed, "It was all my fault, all my…" he struggled at the weight of the realisation, horror struck. All the deaths— Cedric, Sirius, Barty Crouch Senior, Bertha Jorkins… They all happened because he had interfered in Dumbledore's plan! His mistake had killed those people. He wanted to run, to run far away, pound this feeling into the ground with his feet, but he couldn't. He was stuck, here, in this room, in this house just like Sirius had been, until Harry's second big mistake had led to his death. Trapped. He couldn't even scream out his horror— he had to be quiet, not to alert the others. His throat felt tight and his hands clutched at it. He could hear the roaring of his own blood in his veins. He couldn't breathe. On the edges of his awareness, he could hear the other two in the mirror- his counterpart frantic and Snape's slow and methodical. He couldn't make out what they were saying, so completely was he drowning in his own horror.

After a moment, he became aware of his name, spoken in a voice that was calm, yet strong and authoritative. A voice he was used to hearing and obeying, for the most part, in potions class.

"Mr Potter. Harry," Harry felt sick and like he couldn't breathe but he tried to look up, desperately seeking help.

"I need you to focus on my voice," continued the man, seeing Harry's attention shift. "Breathe with us, Harry." He said, making exaggerated breaths, which Harry's counterpart matched.

With difficulty, Harry turned towards the voices, clutching his throat, unable to breathe, sure he was dying.

"Good Harry- stay with me now," said Snape calmly, "Breathe in slowly with me, you can do it. In….. out. Very good, and again."

At length, Harry's breathing levelled out and he felt tears running down his face. He wanted to leave, to get away from these people who'd seen him at his most vulnerable. But what if he couldn't find them again? He wanted to know more, even if knowing more was unbearable. This, though— he'd never had an experience like this before. He felt so humiliated.

"None of that, Mr Potter," came a stern voice from the other side of the mirror, as if Snape was reading his mind, but Harry knew he'd not made eye contact. "You've had a nasty shock. Your response was not embarrassing, nor an overreaction. I want you to stay exactly where you are." Harry nodded, breathing slowly.

"Would you like to know about years two through five?" asked Harry's alter-self, after a moment. At some point he seemed to have retrieved his cup. Or maybe Snape had done it for him, but it was steaming in a way that suggested it had been reheated.

The offer of a story was a clear attempt to distract him, but Harry nodded, not minding, and still not up to talking, as he watched his alter-self get comfortable and begin his tale.

"We also had the Chamber of Secrets open in second year, but when I told Severus about the voice, he worked out it was a basilisk very quickly."

"How…" Harry whispered, still recovering, "Did he know you were a parseltongue?"

"The Slytherin common room is full of snakes," replied Alium-Harry, with a smile. He seemed to smile a lot. "Pictures, statues… Everyone found out in my first year. Well, all the Slytherins did. We don't tend to give information away to other houses unless necessary."

"Anyway, the staff figured out where the entrance was and caught Ginny Weasley in the act of going down there. The headmaster took the diary, and realised that it was a horcrux— a piece of the Dark Lord's soul in a container. He's had a few long conversations with Riddle since he's had it, and he's been looking for the rest of the horcruxes since the diary was discovered."

Harry's breath caught in his throat. "There's more?" he asked, horrified at the thought.

"Unfortunately so," replied his alternate self. "Dumbledore has been able to trick a bit of information out of the teenage Dark Lord in the diary, and Severus has been working with the headmaster; he knows the character of the Dark Lord reasonably well and used his knowledge of the Dark Arts and Riddle's diary to invent a spell that detects the Dark Lord's horcruxes, which is how we found out about a lot of them." He grimaced.

Harry felt slightly ill at the mention of the horcruxes. "How many are there?"

"Seven horcruxes, eight soul shards including himself, we think," Snape supplied. "Ravenclaw's diadem in Hogwart's Room of Requirement, Hufflepuff's cup from Bella Lestrange's Gringott's vault, Nagini the snake, Marvolo Gaunt's ring and of course the diary. We only recently found Slytherin's locket when Harry inherited Grimmauld Place." He gestured around the room. "The seventh, I'm afraid, is…"

"This," supplied Alium-Harry, gesturing helpfully at his forehead. "Don't panic again," he said to Harry, sternly. "That's why we're here, looking through Dark Arts books. We're going to find a way to remove it."

Harry paled, his chest tightening again.

"Breathe, Harry," instructed Snape, his voice determinedly calm despite the look of frustration he sent his ward, who looked very guilty.

For a few moments, there was no sound but that of calm breathing as Harry tried to match his own to that of the Alium Snape, and of whispered reassurances from the other two.

"Am I really a horcrux, sir?" asked Harry eventually, swallowing his nerves.

"In all likelihood," confirmed Snape, calmly, as if he were discussing whether it would rain this afternoon. "However, we are in the process of determining a way in which to remove the horcrux from you without causing harm."

"But it took basilisk venom to destroy the diary!" responded Harry, fighting against his rising panic.

"Yes," agreed the other Harry, "Generally speaking, they can only be destroyed with basilisk venom or fiendfyre. Not so good for us. But we are accidental horcruxes- we were never intended to have the Dark Lord's soul in us in the first place, so it shouldn't be bound as tightly. We were also the last made, so will contain a smaller portion of the Dark Lord's entire soul than the diary did, as it was first. We believe there will be a way that doesn't destroy the host."

"But you've been researching this for years," pointed out Harry, "and you haven't found one yet!"

"We've only known about the scar horcrux for about a year, actually," corrected Snape. "And I assure you, I shall make certain before we part that you have all the pertinent information that I have gathered thus far."

"Thanks." Harry swallowed and changed the subject, addressing alternate Snape. "So, did the hat want us," he gestured between himself and Alium-Harry, "in Slytherin because of," he indicated his scar. "Does it make us…"

"Evil?" Snape shook his head, looking mildly exasperated. "I've told you already, Mr Potter," he continued, softly. "Abused children often sort into Slytherin. It's not a sign of inherent evil. For what it's worth, I've known Harry for five years now, and he fits into Slytherin perfectly, but I know he'd fit into Gryffindor almost as well." Harry nodded and was silent for a minute, before another question made itself known.

The temperature in the room was beginning to rise with the heat of the day, and Harry pushed back his hair from his damp forehead as he spoke. "You said that you think Snape told You-Know-Who about the prophecy in my world. Why do you think that?" Harry asked.

"In the main, because I have no reason to suspect otherwise," admitted Snape, slowly. "There's no way to know for certain aside from asking him of course, but think back- could your version of me be under the same vow?"

Harry considered this. Could Snape have made a vow to protect him? He thought back to first year, when Snape kept him on his broomstick when it was jinxed, then refereed the subsequent Quidditch match. To third year, when Snape followed him and Lupin to the Shrieking Shack on a full moon, despite having nearly faced death in the form of a werewolf there once before thanks to Sirius's prank, then proceeded to put himself between said transformed werewolf and Harry. To fourth year, when Snape argued against Harry's inclusion in the Triwizard tournament, then returned to Voldemort's side at Dumbledore's request to spy. To last summer, where he contacted the Order to send them after Harry in the Department of Mysteries. His eyes widened in shock. Not only was it plausible, it was the best explanation for his seemingly incongruous behaviour.

"Yeah," exhaled Harry, in disbelief. "Actually, that makes a lot of sense."

Snape nodded.

"But," Harry frowned, "Why be so awful to me outside of class? Last year, we had occlumency lessons, just him and me- no observers. And he was vicious. Bellowed at me, "Clear your mind Potter!" without ever explaining how. And he pulled up my worst memories, over and over, taunting and berating me, and I was so angry and humiliated and it just made it impossible! And then he'd point his wand at me and the whole thing would happen again."

"Wow," commented Alium-Harry, after a moment's silent shock, "Your Snape sounds like a total git."

"Language!" rebuked Snape, sharply, "Though I can't say I disagree with your assessment."

He turned his attention to Harry, "I can only speculate, Mr Potter, as my experience of Harry Potter has been completely dissimilar to that of my counterpart and so have our respective actions towards him. However, from my understanding of my own character…" he tailed off, before continuing, somewhat haltingly, "I believe that your mutual enmity with my counterpart may have reached such dizzying heights that he no longer distinguishes you from your father. He likely mistakes your intrinsic distrust of adults and disinclination to ask them for help for arrogance and believing you do not need help. He may, in fact, consider your perceived arrogance as part of the reason for the Dark Lord's return, given your actions in first year."

"And third," volunteered Harry, heavily. "We knocked Snape out in the Shrieking Shack. If we'd not done that, perhaps Pettigrew wouldn't have escaped."

"Perhaps," agreed Snape, "But that is irrelevant to our discussion, and I wouldn't recommend you try out the Alium with that scenario either. This is a dark object, after all, and will draw you in with repeated use. This one excursion into the realm of what-if should not cause lasting harm; nevertheless, I will be destroying our Alium, once I am satisfied that you have some support in your own world."

"I've got support!" protested Harry. "I've got Ron and Hermione, Remus, though he's not around much admittedly, the rest of the Weasleys…"

"Ron and Hermione?" interrupted his alter-ego. "Weasley and Granger?"

"Yes," Harry paused, amazed that this hasn't occurred to him before now, "Wait, who are your friends? Ron would never be friends with a Slytherin."

Alium-Harry scoffed, "You're right there," he said, dryly. "Sorry, I know he's your friend but he's a prejudiced sod. I can't say we get on well. Granger's alright though."
"You know Hermione?"

"Yeah, she's pretty well-known in our year. Narrowly survived an encounter with a mountain troll our first Halloween. Got hit by flying toilet shrapnel but the teachers got there not long after and Pomfrey pulled her through. Bloody Weasley's the reason she was in there in the first place, apparently. She's mostly friends with Longbottom, but we've studied in the library a lot and I keep the prattier Slytherins off her back."

"Are you suggesting that there's such a thing as a non-pratty Slytherin?" Harry joked.

Here though, his alternate self scowled. "I can tell you're best friends with Weasley. Of course there are decent Slytherins! We're not all obsessed with blood, you know. Tracy Davis is a half-blood, like me, and Severus too for that matter!"

Harry had so many questions after this exchange that he didn't know which to ask first. But then, a thought occurred to him.

"Wait, if you're not all automatically blood-purists, why was the Slytherin password in second year 'pure blood'?"

At this, his counterpart looked visibly confused. "Password? What are you talking about?"

"In second year, we thought Malfoy was the heir of Slytherin so we polyjuiced into Crabbe and Goyle and followed him into the common room. He gave the password— pure blood! How'd you explain that if you're not all blood purists?"

His alternate self's expression remained bewildered, "Why would the rest of us have any say over Malfoy's password?"

"Wait," Harry was utterly at sea, "Malfoy's password?"

Alternate Harry's expression cleared. "Ohhhh, do Gryffindors not have individual passwords?"

"Individual passwords?"

"Of course. Slytherins each have their own password, as well as their own bedroom. Something about not relying on others."

Harry's eyebrows lifted in surprise. Their own bedrooms? How was that fair? "So," he said aloud, "you're saying Malfoy set his own password? Makes sense I guess- it's not exactly subtle." He paused, struggling with the idea that Snape, of all people, could be a half blood, but not feeling comfortable enough to ask about it. "Who would you say are the decent Slytherins then?"

"I stick with Blaise Zabini, Tracy Davis and Daphne Greengrass, in the main. Nott's OK too, if quiet."

Harry grinned, "Not Malfoy then?"

"As I said, he's a bit of a prat at times," Alium-Harry returned the smile. "It's not really his fault- I defy anyone to grow up with Lucius Malfoy as a father without being at least 20% obnoxious. We do sometimes hang out though. Used to be more often, but he distanced himself once he started fancying Hermione after the Yule ball in fourth year."

"He fancies Hermione?!" Harry was aghast at the thought of Hermione and Malfoy as anything other than enemies.

"Yeah. Of course he didn't say that— probably can't even admit it to himself– he'd be disinherited if old Lucius heard so much as a rumour– but it's fairly obvious, even without legilimency."

"You're a legilimens?!"

Here, Snape cut in, with a scowl at Harry's counterpart, "I've been teaching Harry since last year, against my better judgement, I might add, beginning once I was satisfied with his skills in occlumency. He is still very much a beginner. And he should not be telling anyone about it."

"You're going to destroy the Alium anyway!" objected Alium-Harry.

"The walls may have ears," Snape said pointedly, directing his most withering glare at his ward, whose own ears promptly went the colour of Gryffindor common room. "But, as I was saying," he directed his attention back to Harry, "Harry has quite a natural affinity with mind magic, which means you do too. I suspect the problem was with the teacher and mode of instruction.

"Occlumency by nature requires a degree of trust between student and teacher, which you and your professor lack. Further, I suspect he did not put the requisite time and effort into considering how best to teach you. When I taught Harry, it took us some time to find mental imagery that worked for him."

"Mental imagery?" queried Harry.

"Harry found that trying to simply think of nothing was untenable." Snape responded. "Eventually, we decided to focus instead on building a mindscape— he built a mental image of flying above the Forbidden Forest. Flying is a diversion, the forest, a shield. He hides his memories and emotions in the lake within it, guarded by the giant squid. To start, you should focus on simply flying above the forest. Lose yourself in the sensation and the visualisation. Imagine the forest so thick beneath you that you cannot see past the canopy of their branches, stretching as far as the eye can see in all directions. You will then require need a teacher for the next part."

"Fat chance of that!" grumbled Harry. "Snape wouldn't teach me again if his life depended on it, and Dumbledore thinks I'm being possessed so won't go anywhere near me."

"Why do you think Professor Snape wouldn't teach you?" queried Alium-Snape.

Here, Harry flushed red, running his hand through his hair. He knew he didn't come out of this story well. "Last year, he had to leave during an occlumency lesson and, well, I… looked-in-his-pensive," he said in an embarrassed rush, feeling very ashamed.

"Ah." Snape said in understanding, looking thoughtful. "Yes, given your history, I imagine he now feels justified in discontinuing lessons. It won't be impossible to convince him to resume them though. After all, he did not see fit to provide you with the opportunity to use a pensieve, did he? By rights he should have done, and by failing to do so, it could be argued that he was effectively in your pensieve the entire time."

This gave Harry pause. "But Dumbledore only has one pensieve, so we couldn't have both used it, could we?"

"Indeed not," came the reply, "However, someone capable of resisting interrogation by the Dark Lord should be able to defend himself from an untrained teenage boy without recourse to a pensieve. Your need was clearly greater."

Harry considered this. Alium-Snape was right, and he suddenly felt far less guilty about the pensieve debacle last year.

"It's his fault that Sirius died!" he declared, angry and relieved all at once.

Snape's eyes narrowed. "Explain your reasoning."

"I've been blaming myself, for not learning occlumency and being fooled by the dream, but Snape didn't teach me properly, so when Vol-sorry-You-Know-Who sent me a fake vision of him with Sirius in the department of mysteries, I fell for it and went there, then Sirius came after me and then…" his throat closed up as he tried to swallow his grief.

Snape and Alium-Harry remained quiet for a moment, an expression of concern and sorrow on Alium-Harry's face, while Harry fought to regain his composure. When he looked up again, he saw two pairs of eyes locked on him. Alium-Harry glanced at Snape, who nodded back to him.

"Harry, for what it's worth, I don't think it was anyone's fault," offered Alium-Harry. "Aside from whoever killed him, of course. We recently lost Sirius too- to a motorbike accident."

"A motorbike accident?" replied Harry, incredulously. It seemed too… muggle.

Alium-Harry nodded silently. "Obviously, in our world there is no Voldemort, was no vision, no incident at the ministry, but… I think it was just his time. He wasn't even flying it," he added, sadness colouring his voice. "I didn't really know him very well- he dragged Weasley into the Shrieking Shack in third year, killed Pettigrew and ran. The Weasley twins found the body; I was never clear on how. We wrote each other letters, but I never met him in person. He died while on the run, and I got a notification from Gringotts saying he'd left everything to me." He shook his head. "I've been trying to get Lupin to take as much as I can- I think Sirius would've wanted that, but he obviously couldn't stroll into Gringotts to change his will. He's refused everything so far, unfortunately."

"...You call him Lupin?" ventured Harry, curious about this difference.

"Yes, well, we've not had much to do with each other personally. He's a decent defense professor though." Alium-Harry shrugged.

"He taught me the patronus charm in third year," said Harry, making circles in the dust on the cloth covering the table.

"Severus taught that to me," said Harry's alter-self. He paused, "What form does yours take?"

"A stag, like my Dad's."

"Ah. Mine's a doe."

"Oh," Harry frowned at the difference. "Why'd you think that is?"

"His mother's patronus was a doe," Snape said, immediately. Harry's alternate self gave Snape a significant look but said nothing.

"What?" asked Harry, puzzled.

"I think it has more to do with my dad than my mum," said Alium-Harry, quietly, under his breath, but Harry heard and so did Severus, whose lips quirked upwards in a small smile as he clapped a hand down on the younger man's shoulder, making eye contact with him for a long moment, but saying nothing aloud. Alium-Harry's face pinked slightly, but a smile found its was onto his face and he beamed at the older man. Snape's reaction, as well as Alium-Harry's initial statement, confused Harry a bit, but he didn't want to risk awkwardness by asking for clarification, so he let it be.

"So, do you think I should try to get him to teach me again? My Snape, I mean." Harry shuddered as his choice of words registered.

"I believe," said Snape, slowly and deliberately, "that I need to speak with my alternate self. I believe that it can be managed under the rules of the Alium- though if I am correct in my assumptions, only you and he will be able to see us here."

"Like the Mirror of Erised?" asked Harry. "Ron couldn't see what I saw."

"Precisely," confirmed Snape, with a perfunctory nod. "You would need to call him here, alone, to avoid confusing the mirror with another potential scenario from a party uninvolved with this one, without yourself leaving the room."

"Why without leaving the room?"

"I cannot be certain that, were you to return, you would see the same versions of us that you now behold. You have the answers to your 'what if' and thus I think it unlikely that the window would connect to these versions of us again. And we have information, pertaining to horcruxes and other research, that has the potential to be incredibly helpful to your battle against the Dark Lord, if there are as many parallels between our respective worlds as I believe there are. I'd like to be certain that at least one adult holds that information in your world, prior to destroying our version of this mirror. Adults in your world do not seem predisposed to take your ideas seriously, so the information coming from me can only help."

Harry was at a loss. "How can I get Snape up here without anyone else?"

Snape thought for a moment. "Is it safe to perform magic in Grimmauld Place? Or do you risk detection for underage magic?"

"I've been told it's safe. We're under Fidelius, but I'd rather not risk it," said Harry. "I've already had one trial by Wizengamot for underage magic; I'd prefer not to risk another."

Snape hummed in acknowledgement. "I could see if my patronus can enter your world. I'll have to deactivate the shield first, to ensure that the magic I exert in casting it may return to me. With your permission, may I try?" Seeing Harry's nod, he continued, "First, do you know where he is? If he is at the Dark Lord's side, this method of getting his attention could ultimately kill him."

"There's an order meeting downstairs," said Harry, by way of permission, and then he watched as a flash of blue once again illuminated the window, before Snape cast the patronus and a beautiful doe cantered out of his wand, through the window, and stopped to sniff at Harry before heading downstairs.

"Oh," said Harry, realisation striking him, turning a shocked expression towards his Alium counterpart, who smiled a tad self-consciously.

Snape raised his hand to squeeze alternate Harry's shoulder once more as he spoke, "And now, we wait."