I borrowed a bit from OotP...it's fun to have new toys to play with. There's no spoiler, just the appropriation of magical innovation.
~*~
"I came as soon as I heard," Harry was saying to Draco as Snape entered the Infirmary, weary after reading James a bedtime story and leaving him entrusted to Dobby and Eleanor. "Has there been any change?"
"Not since I arrived. Mother? You were here first," Draco paused, "well, after Sirius and Remus of course."
Narcissa looked pale and tired. "No change. Thank Merlin George's son was in the office when she collapsed...who knows what would have happened to the bleeding in her brain if Poppy hadn't..."
Sirius looked around at everyone as they discussed Hermione's condition. He felt vaguely conflicted, at the back of his brain, but he knew what he must do. It had been explained so well by the stranger whom he had met that morning.
"All you must do," the stranger said, "is put a simple charm on her brain to expand within her skull, in the left hemisphere. I'll give you a Self-Destructing Parchment with the instructions when I leave. The bleeding effect will be temporary but will render her unconscious for a time. She'll wake up completely cured. And you'll be able to tell her that you did it; the one she rejected. You'll be able to hurt Snape and her for their treachery without actually hurting them at all, at least in the long run."
Sirius was unaware that he had been rendered somewhat more susceptible to suggestion by the stranger, who was someone who had recently become very adept with various forms of the Imperius curse. It didn't do well to be heavy-handed in such delicate matters, of course, but just enough to stretch natural tendencies in the attempt to do something slightly out of character, and to be vague and more accepting than usual of a stranger's advice. With Sirius Black's well known hotheaded temper and his recent angst over the Headmistress, it wouldn't be much of a stretch.
"Then, of course," the stranger continued, "you'll call all her friends to her bedside. All of them, mind you...all of her Spirit-brethren, in particular. They'll all need to be there when she wakes up."
"Won't her Spirit protect her from unusual charms?" Sirius had said, struggling to find a way to do something other than dumbly nod at the hooded figure whose face he never saw, whose name he never would remember.
"Oh," the man said in a darker tone, "Her Spirit has made a fatal mistake and left her body. Don't concern yourself."
Unfortunate, that. Dumbledore had given Hermione a few Chocolate Frogs. The new edition, in addition to having "Hermione Granger, Youngest Headmistress of Hogwarts" and "The Boy Who Lived: Harry Potter" cards, also had the rare foil "Dementor: Guard of Azkaban" card randomly inserted into packs. Hermione had been fortunate enough to get one of the rare cards, and had carelessly left it on her desk after showing it off to Harry and James. Once Eleanor had explained her presence to Hermione, the Dementor on the card (in the way of all wizarding portraits, having the ability to travel to other portraits of the same person or creature) went to tell his brother, who always kept a family photo in his cloak, the news; his brother, unfortunately for the Headmistress, was Voldemort's lieutenant.
And now, everyone that Voldemort despised the most and wanted to visit his vengeance on the most were in one room. All of the Children of the Spirit, except...
James.
Sirius shook his head, and looked nervously around the room. How to arrange this? Snape would never...
Snape. A surge of hatred shot through Sirius Black. Severus sensed it, and looked straight into Sirius' eyes. And suddenly, with clarity, he knew.
"Black," he said quietly, "join me?"
"Indeed," Sirius said in a low voice. He'd use this to his advantage somehow...subdue Snape, and go steal his son.
Harry watched them go with just a tinge of worry, and laid his hand on Hermone's head. Eleanor drifted through a wall just then.
"Narcissa...oh, Narcissa, this is all my fault." The First Lady looked as glum as a ghost could.
"What?"
"The Spirit is not in her anymore...she's with me...it must have been a horrible mistake..."
Everyone in the room regarded each other with horror.
"Could someone have known that she was no longer protected?"
"Well...no one knows...I just told her this morning..."
Harry looked downright panicked, and said: "Where? Where did you tell her?"
"In her office. Why?"
"Oh, there are just about SEVEN THOUSAND PORTRAITS EAVESDROPPING IN THERE...Jesus."
Everyone's hearts sank.
"Fortunately," a voice said from the doorway behind a pair of twinkling blue eyes, "she got a Dumbledore card in her last pack of Chocolate Frogs..."
~*~
Snape had Sirius pinned against a wall.
"You did this, Black. You did it. I can feel it from every pore."
"Believe it or not, you stupid git, I'm helping her."
"I seriously doubt..." Light dawned, and Snape raised his wand. "Finite incantatem."
"What..." Sirius shook his head, "oh, shit..."
"Yes. I recognized that little spell from the bad old days. You've seen Voldemort."
"No, actually...I haven't left the castle, and you know it's enchanted to not allow him in. Not possible..." Black was looking green around the gills.
"Not possible, eh? You've forgotten that Voldemort sleeps in the Gryffindor boys' dormitory now thanks to his namesake child. Did you see your attacker?"
"I...no, I never saw his face..."
"We need to protect James. Now."
*~*
"Dobby," the visitor was saying, "could you fetch me a cup of tea?"
It takes a powerful magic to bamboozle a house-elf, all the hooded wizard was capable of mustering at one time. But in the wink of an eye, James was safely in the cloak of the stranger, and Dobby returned a beat too late. His next stop was the castle walls, to drop the enchantment that guarded the gate against his genetic donor. He could feel his connection to Black was broken, and he would have to speed up the Plan, so it was important to have a hostage. Muttering all the way past the door of the Great Hall, he plowed head-on into George Weasley.
"You!" the hooded figure spat. "Out of bed, after hours? Go back to your dormitory! Now!"
"I wouldn't be a Weasley if I wasn't out of bed after hours, mate. My dad would drum me out of the school if I weren't causing trouble."
Despite himself, the figure in the cloak laughed. And regretted it.
"Errol?" George said incredulously. "But..."
"Stupefy," said Thomas Riddle. As George crumpled to the ground, a softer: "I'm sorry."
*~*
Sirius and Severus rushed into the infirmary. "Oh, Hermione, what have I done?" Sirius said, placing both hands on her temples, then reaching for his wand.
"Stop!" Draco and Harry said as they saw him point the wand at Hermione's head. Dumbledore, the newest arrival, silenced them with a look.
"Finite incantatem." No, it wasn't going to be that easy. And the Self-Destructing Parchment had, well, self-destructed.
"Forgive me, Hermione...Tom Riddle has done it again." Sirius sank to the floor, head in hands. "He said...it would cure her...God, I am an idiot...I just wanted her to love me and when I knew she had stayed with Snape..."
"Now is not the time for confessionals, Sirius," Dumbledore said mildly. "It appears that young James Granger collects Chocolate Frog cards as well. To the Hogwarts gates, everyone... Eleanor, I trust you can keep Hermione safe." No one found this comment odd, but Severus certainly understood what was meant.
Snape looked down at his lover's comatose form again, and looked at Eleanor. "I'll send the Bloody Baron in here as we pass the Slytherin area on our way out. Send him if you have need of us." And much of the group that had, ten years ago, defeated Voldemort, went off to attempt to defeat him again.