Disclaimer: I am not J.K. Rowling. I do not own Harry Potter.
Further Disclaimer: I am not the member known (at the time of the initial post of this piece) as 'Right What Is Wrong'. His/her 'Force Interrupt' series about plot-holes did however in part inspire this particular parody piece.
Note: This is 'parody'. It is rated 'M' to be on the safe side since it features at least one member of the Black family making risqué references. It is (as of February 2021) intended as a one-shot.
The piece opens in an alternate universe in the setting of the 'Spinner's End' chapter of Harry Potter and the Half-Blood Prince, where Narcissa and Bellatrix are questioning Severus Snape about his activities.
"I had sixteen years of information on Dumbledore to give him," Severus Snape said, "when he returned; a rather more useful welcome-back present than…"
"Wait what?" Bellatrix interrupted. "That rat, Wormtail, sought out the Dark Lord the year before the Dark Lord was gloriously restored, and spent almost twelve months with him – and Wormtail had spent the previous dozen years living in the home of a Ministry official, and travelling back and forth to Hogwarts with the blood traitor brood's children. Do you really think that in all that time that Wormtail acquired no information, nor that he did not divulge anything and everything of significance that the Dark Lord required, whilst they were waiting for the preparation for the restoration ritual to come to fruition? Or do you suppose that they sat around talking about quidditch for days on end?" There was a soft pop in the air behind Bellatrix. "And Wormtail himself captured a Ministry official, Bertha Jorkins, whom he brought before the Dark Lord and when Wormtail and the Dark Lord joined up with Barty Crouch junior, freeing him from his father and capturing said father in the process, the Dark Lord gained more information. Do you think that all of these wizards and a witch knew nothing of Albus Dumbledore and his doings? And do you think that there were no back-issues of newspapers which the Dark Lord was able to get Wormtail and Barty to procure? And besides all of this, the Dark Lord himself was at Hogwarts during the 1991 to 1992 school year," Bellatrix's voice rose to a triumphant shriek. "What plausible information, do you think, Snape, that you were able to present to the Dark Lord about Dumbledore that he had not already discovered for himself, a dozen times over, from other sources, before you dared to present your own insolent hooked nose back before the Dark Lord's face?"
There was a soft, insistent, 'thunk-thunk-thunk' sound from behind Bellatrix and everyone turned and shifted to see a young woman meaningfully bouncing a baseball bat in one hand.
"I think," the young woman said, "that we need to cut the author some slack, in the interests of a dramatic turn of phrase. Or else…"
"Oh yes." Bellatrix's eyes widened in an expression of pleasure. "I've been a wicked, wicked witch. Punish me, please."
"Oh dear." the young woman with the baseball bat said. "This isn't going to work is it?"
"This is Bellatrix Lestrange that we're talking about here." Severus Snape observed. "Threats of violence of any kind excite her. Look. She's off in a world of her own already."
And indeed, the dark witch's eyes were glazed, and she was mumbling something about 'Please master: hurt me more. Make me really suffer.'
"Right:" said the young woman with the baseball bat. "Well, umm, let's say that you had sixteen years of highly secret potions research which you'd been doing with Albus Dumbledore, Severus, which Lord Voldemort couldn't have found out any other way and which he was really pleased to hear about. Because Albus worked with Nicolas Flamel, we know, and was really interested in alchemy at at least one time, and you're really good at potions, Severus, so obviously Albus Dumbledore approached you soon after you left school, and the Dark Lord likes to know magical secrets, so of course he wanted to know what Albus had been researching."
"Wait a moment." Narcissa narrowed her eyes. "Sixteen years, counting back from the Dark Lord's restoration in 1995, makes 1979, which was several years before Severus even started teaching at Hogwarts according to what he told that Umbridge woman."
"Look: the author's really bad at maths and Severus was a teen-genius, and do you or do you not want Severus' help for something important, or will I have to find out whether you enjoy the thought of pain as much as your sister?" the young woman threatened.
"I was born a Black." Narcissa said. "And I married Lucius Malfoy. I'm certainly interested in experiencing new sensations."
"The Blacks are all quite mad." Severus said to the young witch. "Why in Hades do you think I wanted to sort into Slytherin after seeing Sirius and his distant cousin James Potter sort into Gryffindor, despite Lily making the pardonable error of thinking Gryffindor to be a superior house on account of the house colours going with her hair? I wanted to be as far away from them as possible." He returned his attention to Narcissa. "I believe that – so long as you promise never to speak to this of anyone else, Narcissa, I can tell you exactly what information I had acquired on Albus Dumbledore , from 1979 onwards, which the Dark Lord was so anxious to discover, and which I could not have disclosed to him at any time before 1995 – not even in the period between 1979 and his unfortunate defeat in 1981." And he bent in close to whisper something to Narcissa, which only she could hear.
"Oh." said Narcissa, as Severus proceeded. Then: "Oh! Did he really? Oh?" (An eyebrow elevated at this point.) "You surely do not say…" And then she flushed and let out a combination of a giggle and a mortified gasp of embarrassment. "Oh, really! No, surely not!"
And a few more whispers and Severus was done.
"Well?" Severus asked. "Is that sufficient?"
"Oh yes. Umm. And not a word to anyone, because the Dark Lord would definitely kill me, in a slow lingering fashion, if he knew I knew that." Narcissa said, trying to pull back together the remains of her dignity.
"You can go away." Severus glanced at the young woman with the baseball bat. "It's all sorted out now."
As mentioned in the opening notes, this parody one-shot was inspired by the 'Force Interrupt' series by 'Right What Was Wrong'. Ariana showing up to threaten a character who has spotted a plot hole in J.K. Rowling's original work was a feature in some of the 'Force Interrupt' series entries, and the 'Force Interrupt' series is certainly where I came across the idea.
I leave it to the imagination of readers to come up with their own versions of what Severus Snape might have had 'sixteen years of information' about, concerning Albus Dumbledore, which would make Narcissa blush and giggle.