The first Astronomy class and the Stargazing incident

 It seemed like everything but the night sky had faded away. As Oleandra stood there in the darkness, eight of the myriad stars started glowing brightly. Without warning, colours flooded the world again as her Mystic Eyes (as she had finally decided on calling them) activated by themselves. 

Fascinated, she watched as light surged from seven of the points, streaking madly towards the central eighth point, forming the Boötes constellation!

Call my name, it seemed to be saying. 

"Odala…" whispered Oleandra. "Inheritance … the final rune…"

Oleandra had never learned about ancient runes before, but somehow, she had just known its name.

Suddenly, the world spun; the sky was falling! One by one, the twinkling stars in the firmament started falling towards her! Oleandra's mind started filling rapidly with complex knowledge she had no way digesting!

Oleandra screamed and fell to the floor, holding her hands above her head as if to ward off the falling stars. The last thing she saw before blacking out was a distressed Professor Sinistra running towards her, wand out…

And then there was nothing but darkness, save for three faintly glowing graphemes; Naudhiz, the distress rune; Elhaz, the protection rune; and Mannaz, the human rune…

 Oleandra woke up in the hospital wing and looked around with bleary eyes. What on earth had just happened to her? Where was she?

Seconds later, Madam Pomfrey, the nurse, was at her side.

"What on earth are they having you do in Astronomy!? And on the first week, too! Usually, the worst I get is a black eye from students accidentally poking their eyes with telescopes, but this one takes the cake!"

"How are you feeling?" she asked, more gently this time. "Is there anything I should know? Any medical conditions? Do you know what happened to you?"

"N-no… But I'm fine now. How long have I been sleeping?" asked Oleandra in a faint voice.

"You've been in a coma for 36 hours," responded Madam Pomfrey.

"Knock-knock," said Dumbledore out loud, imitating a door knocker.

Unknowingly, the headmaster had appeared in the doorway.

"May I visit Miss Greengrass?" he asked calmly.

"Absolutely not," said Madam Pomfrey. "She needs her rest!"

And upon saying these words, she shooed the headmaster outside unceremoniously, then stepped out and closed the door behind her.

Daphne, who had been waiting outside all morning, asked anxiously, "What's happening to my sister? Will she be all right?"

"She's just come to," answered Madam Pomfrey. "I've run all the tests, but they've all come up negative. It's not a disease, and it's not a curse either. You're her sister, do you know if it could be a blood curse unique to your family?"

Daphne shook her head. "No, but my little sister Astoria has one."

And thus, it was settled that it was simply a case of frayed nerves and acute anxiety.

But Dumbledore thought differently. He had secretly checked her earlier, and she had been exactly like a victim of the Dementor's Kiss. In other words, she had no soul! Moreover, he had tried to use Legilimency on her when she had awakened but all he read from her was a low humming sound, as if a thousand bees were lodged inside her skull. 

Normal Occlumency would have at best blocked the invasion, or offered fake memories for him to read. This was very strange indeed, as even regular Occlumency was not something an eleven-year-old girl should know.

It just so happened that this was the year that Harry Potter had come to Hogwarts and that Dumbledore had accepted to hold to the Philosopher's stone for Nicolas Flamel! This could not be a coincidence, he reasoned. 

Despite being the greatest white magic practitioner in the world, Dumbledore was perhaps one of the most knowledgeable wizards about the dark arts, second only to Voldemort! Therefore, if Dumbledore didn't know what had happened to the young Greengrass, then it stood to reason that it must have been Voldemort's doing! Moreover, she was a Slytherin. Who knows if she had been tempted by the dark arts…

But even the greatest wizard can sometimes be wrong. Yes, Voldemort had infiltrated the school. However, Oleandra still had her soul, it was merely being protected by Naudhiz, Elhaz and Mannaz, an automatic defensive measure to safeguard her soul from being denatured by the torrent of information coming from the stars. 

After all, how could have Dumbledore guessed that she had been using an extinct form of magic that predated Hogwarts by at least 300 years, thought by most to merely be a form of writing for ancient wizards? She had nothing to do with You-Know-Who's plot to revive himself using the elixir of life!