(Author Notes updated 4th January, 2015)

Disclaimer: I am not J. K. Rowling. I do not own Harry Potter.

Note: This story is set in an alternate universe where Lily Potter gave birth to twins on the 31st July, 1980. That is the initial point of divergence, but it is a touch loose in its adherence to canon on some points. This story is rated 'M' to be on the safe side. This is a one-shot.

Further Note: The exchange between Severus and Albus of the 31st October, 1981, from "You! You promised!..." through to "...for your actions?" is very loosely paraphrased from an exchange viewed in a pensieve in 'The Prince's Tale" chapter of Harry Potter and the Deathly Hallows.


31st July, 1980

"I am going to kiiiiiill you for this James Potter", Lily screams from the adjacent room where she is confined with the midwife. "If you are ever in the same room as me again in anything remotely resembling a state of undress I am going to…" She breaks off into muffled swearing.

"Do you think she's alright in there?" James looks guiltily at Sirius.

"It's twins, mate, and you're to blame." Sirius smirks. "You'd better hope she is alright, because you're going to have your hands full if she isn't."


30th August, 1980

"NO!" James bellows. "Absolutely not! I will not countenance it!"

Lily, despite currently having her arms full with Harry James Potter and Angelica Snapdragon Potter still manages to subject James to a withering glare.

"You've got Sirius for Harry. I want Severus for Angelica. He may have been a bit rude to me in the fifth year at school, and have given you a hard time throughout, but he was my first real friend in the wizarding world."

"No, no, no!" James bellows. "We don't know for certain, but even if he's not one, he's practically a Death Eater!"

But though he rants and raves and begs and pleads, Lily Potter, formerly Lily Evans, is an immovable object once she sets her lips like that.

Lily can do maths and has very real, pragmatic reasons for wanting Severus Snape involved with her children. Given he was caught eavesdropping when Trelawney was delivering it, it doesn't take an idiot to figure out that it was probably Sev that tipped Voldemort off as to the first part of the prophecy which Voldemort has (at last) decided refers to Harry; but she also knows that a week or so ago just after an Order meeting Albus Dumbledore had a secret rendezvous with Severus, and the next morning Albus told Lily and James that they were now Voldemort's number one targets. Severus Snape cares about them, or at least her – enough to betray his master's wishes and put his own life at risk to bring a warning – and that sort of responsibility and terrible devotion is something she wants protecting her children.

Eventually James caves in, with a line of muttered threats, conditions, and promises that he wants Lily to extract from Severus. Now all Lily has to do is find and break the news to Severus. And make sure he understands that she wants this kept secret until the current war is over, because she appreciates he can't tell his current master he's just become the godfather of the sister of a boy his master may well end up trying to hunt down and kill. Well at least not without putting himself in an impossible position…


31st October, 1981

An argument is already raging in the headmaster's office at Hogwarts, when a devastated Severus Snape walks in.

"And I'm telling you, Albus, you can't just dump a pair of children on a muggle woman like this, even if she is Lily's sister." the deputy headmistress is shouting at the headmaster.

"Be reasonable, Minerva: Harry's godfather has disappeared, as has Peter Pettigrew, and I can hardly place the boy who has rid the world of Voldemort with a werewolf, the Potters' other closest friend… I might approve of Remus, but it would be politically impossible with the Ministry right now." Albus argues. "They think that all werewolves are just like Fenrir Greyback – and like Fenrir Greyback, are therefore Voldemort supporters."

"And I'm telling you, raising a child is expensive – probably doubly so for a muggle. You can't just…"

And at this moment, feeling gut-wrenchingly awful, Severus raises his voice to add his own complaint to an argument which looks from the colour and sweat upon the faces of those involved as if it has been raging for some time.

"You! You promised! You promised you would keep them safe!" Severus glares at the headmaster, lacing his voice with every bit of the hurt and loss that he feels.

"What is this, Severus?" Albus Dumbledore takes the line of attack of guilt-tripping him right back. "Can it be that you actually feel some kind of regret… remorse – even – for your actions?"

"I… I want to…" Severus trails off. In the corner, in two transfigured cots, presumably shielded by silence charms from the adults shouting at one another, are a dark-haired boy and a red-haired girl. The boy has Potter's messy hair – even if it is not in Potter's colour – and it doesn't take a genius to figure out, given the events of tonight and the argument raging when Severus walked in, as to who these two children are. This is the first time, despite Lily's arm-twisting of a year ago, that Severus has actually seen the Potter children in the flesh. The girl – although her brother has them too – has Lily's green eyes.

The headmaster, convinced he has quelled Severus, has returned his attention to his deputy.

"Well in that case we'll have to split them up then." he says. "We can place Harry – who's more important, as the child of prophecy – with Lily's sister and pass the girl on to an orphanage or maybe a wizarding family that's lost a child in the war."

"Right: so Harry and his sister have lost whatever other immediate magical family they had, so now you want to take them away from each other!"

Minerva, when she's angry, Severus vaguely notes, is capable of achieving a level of venom and scorn in her voice which surprises even him.

Severus continues to stare at the red-haired little girl in the corner.

"Minerva: it's the logical thing to do, given the situation." the headmaster says in a calm voice, clearly intending to grind her into the ground with a rational line of attack. He adopts a slightly conciliatory tone. "Now, there are some things I need to check and put in place around Lily's sister's house, which will take me a day or two, and since we're going to have Harry up until then, we may as well…"

"Lily asked me to be Angelica's godfather." Severus intrudes upon the situation. Suddenly he has the attention of both the headmaster and the deputy headmistress. "I agreed. We kept it secret given the difficulties it might present if it became known. I will give an oath upon the severest magical penalties should I lie that this is true, and provide memories for pensieve inspection if required. Unless there are any other known wishes of the Potters to the contrary, I exert my rights and duties as godparent and – absent any indication that as her closest adult blood-relative Petunia wants her – I claim Angelica."

A sudden awful silence descends.

"Severus. Would you be prepared to take Harry as well?" Minerva asks, an odd note in her voice.

"You can't do that." the headmaster says a little too quickly. "Harry has to live with a blood relative of his mother. There are certain protections, if I am fast enough to act, that I can effect to secure his safety, and Lily's sister is…"

"Headmaster: If Harry has to be with a blood relative, then that is an argument against splitting him and his twin sister up.", the deputy headmistress says.

The headmaster opens his mouth to make some retort to that then frowns and closes it again as if Minerva has made a salient point. Then, like Minerva, he turns his attention to Severus.

Both of them are looking at Severus, waiting for his response on this, but Severus is ignoring them and looking at the girl in the corner, trying to think of what is in her best interests.

"I can put up with the brother, too, at least until Black can be contacted and asked if he wishes to accept his duties." Severus decides. "Since I am currently at Hogwarts acting in the capacity of potions master, perhaps Black would be amenable to staying at Hogwarts too, to assist with teaching Defence, if it is necessary to keep the brother and sister together for the purposes of protection. Black has auror ambitions, after all."

Severus is also interested to see whether Black would be capable of surviving the jinx believed to affect the Defence Against the Dark Arts position…

"Albus. Keeping them under our roof here at Hogwarts for most of the year, being raised by teachers, would mean you could keep a close eye on them and ensure their safety personally." Minerva seems keen on the idea.

The headmaster adopts a calculating expression, apparently running various scenarios through his head.

"Well, it would seem to be what is for the best for everyone." he eventually concedes.

"One more thing, headmaster:" Severus requests. "If, should the Daily Prophet happen to contact you about this, you could emphasise that Harry is the only known survivor of a killing curse? I gather that Alastor Moody has already investigated Voldemort's wand, and ascertained that he only cast three killing curses after putting a dark mark and anti-apparition wards up – presumably the ones over the Potter residence – which suggests to us he didn't actually get around to trying to kill my god-daughter. Nevertheless, if you put the 'only survivor of a killing curse' line out there and as a result the press wishes to jump to the incorrect conclusion that Harry was the sole survivor of the attack on the Potters, that would make things much easier for me when it comes to protecting Angelica. It will make people less inclined to connect her to the Potters, for example, should I pass her off as someone else."

"That's very Slytherin of you, Severus." the headmaster says. "On this occasion, however, I happen to agree it could be useful. I won't actually lie to the Prophet but I'll certainly put that 'only survivor of a killing curse' line out there, and use my influence with the ministry to see any auror reports are buried deep and sealed. The faster and deeper we make both the Potter children disappear, the easier it will be to keep them away from any Voldemort loyalists who survive their master's fall."


2nd November, 1981

The news that Sirius Black had apparently blown up a street full of muggles and Peter Pettigrew, resulting in Sirius' being sent straight to Azkaban without trial, upon capture, of course nailed shut the coffin lid on any immediate possibility of Sirius Black taking responsibility for his godson. By that point, since Severus had dealt with all legal paperwork necessary to assume responsibility as guardian for Angelica (including obtaining a signed note from Lily's sister saying she wanted nothing to do with raising any surviving children Lily had), the headmaster was able to make a good case to both the ministry and to his potions master that Severus should assume responsibility for Angelica's brother, too. And thus the fate of Harry and Angelica Potter was sealed, although Severus was disturbed by quite how placidly the headmaster took the news of Sirius' crime and being sent straight to Azkaban without even a trial. Apparently the headmaster considered that the fewer people he needed in on how he was making the Potters vanish, the better, and a Death Eater godfather who had betrayed the Potters and was in Azkaban for it was clearly the last person the headmaster had any duty to let in on what was going on. And maybe – just maybe – the headmaster had recalled the occasion during Black's school days when Black had plotted a late-night encounter for a fellow pupil with a ravening werewolf, and he had now concluded that evidence of Black's bad character had been there for so long that a trial wasn't really necessary…


5th November, 1981

By the end of the fifth morning after that fateful Hallowe'en night, it was all over. With Albus Dumbledore expediting the paperwork, Angelica and Harry Potter had both been formally adopted by Severus Snape, and their family name changed to Snape – although in the interest of hiding them and with the assistance of one of Albus' contacts in the auror department, false names and destinations for the children ended up on all the paperwork filed in the ministry's official archives. A discussion between the headmaster, the deputy headmistress, and Severus saw them conclude that nonetheless, with the children around Hogwarts, some of the staff who had been around either of the children's parents were likely to notice similarities at some point and that Hagrid, at the very least, although well-meaning was sufficiently loose-lipped (absent any magical incentive) to be considered a security risk. It was decided, as additional security, to thus institute a fidelius charm to protect the information that Angelica and Harry Potter were now Angelica and Harry Snape. There was a good deal of discussion as to who the secret keeper should be, and in the end it was decided that Severus would be it, but that Filius Flitwick the head of Ravenclaw and charms professor would cast it – and that the headmaster, the deputy headmistress, the head of Hufflepuff, Hagrid, and the school nurse would also know it. Severus agreed that at some point, he would inform Angelica and Harry.

That was intended to be it, until Filius pointed out that there was of course the matter of the Potter money stored with Gringotts, and that the goblins might not unjustifiably be unhappy if a fidelius were to prove capable of hiding a client from them. Filius was asked to institute inquiries with Gringotts with all due speed.


8th November, 1981

The evening of the 8th November saw Severus Snape, his adopted children, and Filius Flitwick assemble in the director's office in Gringotts, with the director and the Potter account manager. Severus gave a solemn oath to notify the goblins as soon as possible after the spell was cast of where the Potter children were, then Filius cast the fidelius charm, and then Severus informed the director and the Potter account manager, letting them into the circle of those who knew the secret. Severus and Filius then took the children back to Hogwarts, where the other agreed upon staff members were formally let in on the secret. As an afterthought, Severus arranged an appointment with Alastor Moody, figuring that it would make sense to have someone in the auror department who knew, and that Moody, a member of the Order of the Phoenix, would make as much sense to tell as anyone else. The tough auror hardly liked Severus, and Severus for his part wasn't exactly fond of being in the other's presence, but he did at least respect him and his abilities.


9th November, 1981

The children were finally starting to settle, to Severus' relief, despite the continuing absence of their parents and their change of setting. Angelica, of course, was adorable – even when she had thrown tantrums or had sunk into long periods of sobbing during the past week or so – but even her brother, Severus had to grudgingly admit, wasn't quite so bad as he had expected of a near-lookalike spawn of James Potter.

Perhaps it the sense of the fidelius which bound them together now under one secret that was helping to adjust their attitudes.


17th November, 1981

Six days earlier, Severus Snape had noticed a slight difference in terms of the colour of his eyes, as flecks of another colour began to appear. By this point they had definitively changed colour to a very dark green. Fidelius charms didn't normally do this to their secret keepers. It was, therefore, likely to do with the children he had adopted – or that in combination with a number of other factors. It had occasionally been known, in the magical world, for adopted children to come to resemble their new parents in slight ways. Apparently in this circumstance it was also possible for it to go the other way.

The whole of Slytherin house had noticed it by now, but they were fine with it, as it made sense to them having a head of house whose eyes were practically Slytherin green.


25th December, 1985

Several years had passed. Occasionally the Daily Prophet reported a sighting of 'The-Boy-Who-Lived', somewhere usually completely bizarre such as Moscow or Timbuktu. The Quibbler occasionally ran elaborate conspiracy theory stories; their most recent one had been one whereby Albus Dumbledore was in league with Great Cthulhu and a cabal of jelly bean manufacturers, with Harry Potter chained in a laboratory somewhere being forced to test the flavour of different new products. So far neither paper had come anywhere close to Angelica or Harry Snape and their 'Unca Severus'. By this point it was also becoming entrenched in the public opinion that only 'The-Boy-Who-lived' had survived. In some of the increasingly fallacious 'historical' texts being released it was assumed his sister (often not even named) had expired along with her parents.

That was good. It made life much simpler.

Severus Snape had by now had to explain to the children, as far as he was able to do so, that they had once had other names, because that idiot Hagrid had of course blabbed about how he had known their parents. Hagrid might be unable to mention the names, as part and parcel of this particular fidelius, but he had still disclosed enough to get them asking questions which only Severus, as the secret keeper, had been able to answer. He had had to explain the basics regarding who had killed their parents, and that said killer might still have followers out there with grudges, hence the name changes and security. Angelica was horribly bright and had pushed him for details that ordinarily only a child a year or two older might have gone after. Harry was happy just to sit there and listen to the discussions.

Severus was by now somewhat worried about Harry's scar. There were residual traces of dark magic in it, but unfortunately they were traces which Madam Pomfrey and Albus Dumbledore between them were unable to do anything about it. In the days around Hallowe'en, or around objects or areas of strong dark magic Harry tended to have nightmares and to complain at times that his scar was aching. It was interesting to note that apparently his sister's touch could neutralise this – especially if she cuddled him or kissed it better. A couple of times Severus had caught the headmaster eyeing Harry with an almost predatory look when Harry's scar had been under discussion, as if he had some idea of what specifically was going on, and had intentions to exploit it if at all possible. Severus had pushed the old wizard on this, but he had twinkled and chuckled, and refused to 'give voice to unfounded suspicions'. Fine. If he wanted to play it that way, Severus would simply have to keep a doubly careful eye on the coot, to ensure the headmaster could not exploit Severus' adopted son.

In the meantime, the headmaster, it turned out, had for some reason been in possession of James Potter's infamous invisibility cloak, and he had taken the opportunity of this particular Christmas to send it to Severus 'to look after until they come of age'. Apparently it was intended as a peace-offering to Severus or a bribe to distract him from harassing the headmaster quite so much about the scar. Severus had unwrapped it in front of the children, not knowing what it was, until it was there to see, and they had insisted he try it on at once, expressing cynicism that a cloak could make someone vanish. They had duly been impressed, and Severus was toying with the idea of perhaps – once they were old enough to be able to sneak around the castle without supervision – to loan them the cloak on occasions if they promised to act responsibly. It was a surprisingly roomy cloak, able to accommodate maybe two or even three adults, and certainly a couple of children (or an adult and a couple of children). Or he might take them out on patrol with him, under its cover, during term-time so that they could see exactly what some of the pupil denizens of the castle got up to – as an object lesson on what they were not supposed to do, naturally.


1st January, 1986

Severus had been out on a practice patrol, on his own, last night, under cover of the cloak making sure that the few students not spending Christmas and New Year elsewhere were behaving themselves, and getting a feel for how the cloak felt and what chances were offered of being spotted. He had had the strangest sensation at times of a tingling of the hairs on the back of his neck, as if someone were blowing on them or stroking them.

Replete from the earlier staff New Year party, he had eventually retired to bed and simply collapsed, without taking the cloak off, to find himself tangled up in dreams of Lily, some of them bordering on outright indecent.

The next morning, getting up, wearing the cloak and partially invisible still, he had thought for a moment he had caught a glimpse of her in a mirror, looking over his shoulder, but of course she wasn't there.


28th January, 1986

Severus had been experimenting for several weeks now and discovered that dreams of Lily corresponded to whether he was wearing the cloak when he fell asleep or not, and that they got stronger if he wore the cloak more nights in a row. He checked the cloak for jinxes, curses, or any other possible signs of magic except the obvious, dark or otherwise, but found none, so he continued to wear the cloak to bed.

In the early hours of the 28th after having had one of his most vivid dreams yet, he woke up, longing to se her once more, and saw her there, in the mirror, instead of his own reflection.

She waved at him.

"Lily?" he whispered.

She mouthed something at him – legilimens – and feeling slightly ridiculous he tried to employ legilimency on the 'reflection' in the mirror.

Hi Sev, she thought at him.

What's happening here? How can this be?

The cloak has, umm, strong ties with members of the Potter family, living or dead, and the link between you and me is strong enough that with the time you've been wearing the cloak asleep now I've been able to cross over and I'm haunting you, personally, Sev. Don't worry. I just want to make sure the children are okay, and I doubt the other castle ghosts will normally be able to notice me, since I'm not exactly a regular ghost as such. I don't think anyone BUT you will be able to notice me in fact, in the usual way of things. Although that unfortunately means there's something I'd *like* to sort out, but can't: I see that they sent Sirius to Azkaban for betraying us, and there could be a problem there. Peter Pettigrew was our secret keeper, not Sirius. It was Sirius' idea. We switched at the last minute but let everyone think it was Sirius still. Peter even had a spell to mimic Sirius' handwriting when he wrote notes about where we were. And I was, uhh, wondering…

Severus didn't mind the idea of Lily haunting him, though he hoped that James would stay wherever it was he currently was. He saw an immediate problem with her desire to get Sirius out of Azkaban however:

Sirius was sent to prison for a bit more than betraying you. He was engaged in some sort of scuffle with Peter and as well as Peter a dozen bystanders were killed. He probably figured out Peter had betrayed you and went after him and was a bit too violent in his attempts to take Peter down.

He didn't even get a trial, Sev. He should have at least been able to make his case, and if he was going to go down done so at least having been properly convicted.

Lily. I'm hardly in a position to demand a trial for Sirius – especially not on the basis of something as flimsy as something I've 'heard' from a ghost which is haunting me personally, which others might well say is just a figment of my imagination, and certainly not given I'm trying to keep as low a profile as possible and keep Angelica and Harry safe.

She pouted.

I guess not. Still, you're doing a great job so far, and it was very generous of you to take Harry on too. I couldn't have expected that of you. Good idea on the name change and fidelius by the way.

Lily. You seem to know everything I've been doing involving Angelica and Harry. I'm worried now about whether you've somehow compromised the fidelius. Do you know about them because you've been reading my mind, because you're not exactly alive, or for some other reason which means that it doesn't seem to affect you? The regular castle ghosts don't seem to have been able to make the connection.

Oh, we're very intimate right now, Sev, given what we've been doing in your dreams. She giggled. Right now we're so closely entwined that I'm practically an extension of you. At the start, when I was crossing over, I wasn't quite sure what you'd done. I could feel you were connected to my children somehow, but whenever you weren't thinking of them, the fact you were looking after them sort of disappeared and Angelica and Harry just became to me a couple of children you'd adopted who seemed vaguely familiar for some reason. It was like looking for something you know is there, but not being able to find it. Don't worry. I think the fidelius is safe enough unless someone else tries to invade you this way, and right now, being in possession, I'm going to fight very hard to keep anyone else out.

Should I let the children know you're sort of around now?

No. She was very firm on this and she saw him frown. I have my reasons. It's not safe right now, for the poor things. And don't you dare go telling anyone else. Hopefully it'll be alright for the children to know at some point in the next few years, at least that you occasionally contact me, but I don't want anyone else involved in this relationship. Well not anyone who you'd agree to… She giggled again. Apparently becoming a spirit had done something twisted to her sense of humour.

Severus sighed and broke contact. He stopped thinking of Lily, and saw only his own image in the mirror. This was going to get very interesting, and not all of it necessarily in a beneficial manner…


Author Notes:

As indicated in the opening notes, this story deviates from a perhaps strict interpretation of canon on some points.

Lily, as mother-of-twins in this story, is perhaps somewhat more pragmatic, calculating, and manipulative, at least when it comes to her children, than her canon counterpart. She also happens (as a piece of artistic convenience, otherwise this would end up being a somewhat different story) to be in the right place at the right time to figure out that Severus Snape is apparently prepared to take considerable risks on her count, despite the fact that she hasn't had anything to do with him for years, and to endeavour to turn that to her advantage vis-à-vis her children. And I'm reasonably certain she could wrap James around her little finger, to get her way, when it comes to one godparent...

In canon when Severus Snape comes upon Albus Dumbledore in the immediate wake of the attack on Godric's Hollow, the scene (at least as it plays out in 'The Prince's Tale' chapter of Harry Potter and the Deathly Hallows) just involves him and Albus Dumbledore. In this story he arrives in the middle of an argument between Minerva McGonagall and Albus Dumbledore about what to do with the Potter children. This is another thing which has gone differently from canon in this universe-where-Lily-had-twins.

I have a sneaking suspicion that whatever it was that Albus Dumbledore did at Privet Drive involving powerful magic (supposed to extend canon Harry's 'protection') may have actually had to do with Petunia not just being Lily's sister, but actually number four Privet Drive being 'her house', but for the purposes of this story I've assumed that whatever magic it is which Albus wants to do would be satisfied with Harry being 'under the same roof' as Angelica for a certain minimum amount of time every year.

Sirius being an auror is something fairly popular in Harry Potter fanfiction; since I'm not aware of any mention of his ever having been an auror in canon, rather than having him actually be an auror in this story, I've made reference to him having ambitions to some day be one. For the purposes of this universe, Sirius tracked down and had his confrontation with Peter relatively fast.

I'm unclear on the precise of mechanics of how the canon 'fidelius' charm works. As far as I understand it, it's supposed to protect secrets', so for the purposes of this story, I've assumed it can be extended to cover hiding an identity.

Harry Potter ended up with a piece of Voldemort's soul attached and sacrificial protection as a result of the events in Godric's Hollow on Hallowe'en 1980. Angelica did not suffer/benefit from either. Harry having a capacity to speak with snakes is not something that has ever come to Severus' attention, by the time this piece ends in January, 1986.

Having the children around (especially his adorable, cute, goddaughter) results in Severus Snape becoming not exactly 'softer' or 'cuddlier' than canon, but a touch more mellow, perhaps...

It's popular in some types of Harry Potter fanfiction that adopted magical children end up resembling their adoptive parents. I thought I'd flip that on its head here, and have the adoptive parent (Severus) coming to resemble the children, at least in eye-colour. And maybe, just maybe, it's an early sign of Lily trying to 'cross back over' - which she finally manages to do, several years later, when Severus comes into possession of one of the Deathly Hallows, facilitating her passage by his contact with it. (In theory James could have tried to 'cross over' too, but Lily and James had a discussion in the afterlife, and concluded that James attempting anything like this might be somewhat more strenuously resisted by Severus; also, possibly the Lily-having-sacrificed-herself-for-Harry thing might give Lily an additional link to the world of the living which would make it easier for her to make the crossing.)

Lily doesn't want it mentioned to the children that she's 'around' at present, because she can sense that Harry's got some sort of connection to Voldemort, and she's worried about the information of her sort-of-presence getting back to Voldemort somehow in consequence if Harry knows. Lily's hoping that whatever connection it is that Harry's got to Voldemort will be dealt with soon by Albus Dumbledore, or simply overloaded and terminated by Harry actually being brought up in a loving environment.

This story is a one-shot.

Update (17th December, 2014)

It's occurred to me that at least as far as normal genetics go, if James Potter has brown hair, and his wife Lily has red hair, then it should (under normal genetics) be virtually impossible for these two to have one child who has black hair and one child who has red hair. As far as this story is concerned, it's magic that they do. (Maybe the red hair gene isn't recessive in this universe when it comes to witches & wizards.)

Update (30th December, 2014)

As far as I can determine, the fidelius charm of canon 'protects a secret', practically infallibly unless the secret keeper discloses it. In this universe Severus wants it kept secret that his adopted children are in fact Angelica Potter and Harry Potter. My reasoning here is that application of a fidelius charm (as it seems to me that it might work, in this universe), to protect this secret, renders it absolutely impossible for anyone to realise that Angelica Snape and Harry Snape are in fact Angelica Potter and Harry Potter. Yes, observers might very well know that Severus has adopted the children from somewhere (he hasn't tried to hide that he's adopted the children). Yes, observers who remembered Lily Evans/Potter might notice the children had the same colour eyes as she did. Yes, if word had somehow got out (and I would assume that if it did it would likely only have come from Albus Dumbledore or Rubeus Hagrid) about the odd shaped scar that Harry Potter had acquired on Hallowe'en 1981, then observers might notice that Harry Snape had a scar which 'looked a bit like that one The Boy Who Lived is said to have'. No, observers will not be capable of actually bringing themselves to believe, despite whatever evidence may be presented to the contrary, that Angelica or Harry Snape are actually Angelica or Harry Potter. Not unless Severus Snape actually tells them.

For the purposes of this universe there are a couple of exceptions to this. First, a spirit 'possessing' Severus Snape could become aware of the secret. By the end of this piece Lily Potter is very firmly entrenched in Severus, and is going to strenuously resist any efforts by anyone else to 'join in' (except possibly efforts by James, but Severus would do his best to stop that).

Second, it seems to me a case might be made that Lord Voldemort may be able to discover the protected identities, once Harry has been told the secret, whilst Lord Voldemort still has a piece of his soul stuck in Harry. To my mind that would require the sort of concerted attack/'rummaging' through the connection by Lord Voldemort which I understand he launched during the 'Order of the Phoenix' canon year, and it would remain an option available to Lord Voldemort only whilst he still had a piece of his soul attached to Harry. It would also presuppose that Voldemort had decided to mount such an attack on someone that he only initially knows as 'Harry Snape' in the first place.

That's the best that I can do at the time of this update to try to clarify the use and function of the fidelius charm in this story.

Update (4th January, 2015)

The fanfiction member known (at the time of this update) as 'Fedora Ferret' did at one point have a couple of 'Harry Granger' stories posted on this site which, if I recall correctly, employed a similar Fidelius use to hide Harry's identity. At the time of this update, according to Fedora Ferret's profile, those stories have been withdrawn for possible revision.