DISCLAIMER: If you recognise anything here, I clearly do not own it. Principal ownership resides with J.K. Rowling and associated entities. I assert no ownership to anything except the arrangement of the words used herein into sentences.
Saturday 22nd October 1977, Hogsmeade, Scotland
The figure blinked into existence near The Shrieking Shack. They were wearing Unspeakable robes, and it was next to impossible to tell their age or sex. They reached a gloved hand into their sleeve and withdrew a wand. It was made of walnut, 12¾ inches long. The figure cast a Calentempus. They looked at the result and visibly relaxed.
They cast a Patronus. Not a fully corporeal Patronus, this was a rapidly shifting blob. It headed off towards Hogwarts. Then they headed into the Shack.
Apart from the House Elves, the Hogwarts kitchens were empty. The mutating blobby patronus appeared in the middle of the kitchen and spoke "To the Hogwarts Head Elf. I am at The Shrieking Shack, and would like to talk to you at your earliest convenience"
the elves looked at each other with curiosity. The Hogwarts Head Elf popped away from the kitchen.
Eventually the figure reached an agreement with the Head elf. Five elves to help with cleaning, and two to look after the house while it was being used. Negotiating for the food was far harder. Elves are, of course, superior to witches and wizards in arguing.
The agreement having been reached, the figure and the elf popped away to somewhere else. The chosen location was dreary and dusty. "It will do" the figure said bluntly "Can you do it with five elves, or do you need more?"
"The job will be done by Monday. Is there anything else Dilly can help you with?"
"I need to send some letters. Can I use the school owls. Most of the people are in or near Hogwarts"
"Yes, call Fluxy when you have the letters"
"Thank you" the figure said, and Dilly popped away. The figure looked around and spoke to themselves "Hmm, letters first, or the wards?"
There was a considerable pause before the figure spoke again "Letters"
Later that day, twenty owls left the Hogwarts Owlery. Eight of the letters went to different parts of Hogwarts. One went to Hogsmeade. Seven letters went to Ministry employees, and one to Diagon Alley.
The letters were identical:
Dear Friend,
~A little knowledge is a dangerous thing~
~A lot can change the world~
~A single pebble can start an avalanche~
~But once the avalanche has begun, it is too late for the pebbles to vote~
This is an invitation to a discussion held on 29th October, 1977. This letter is a portkey. The activation phrase is 'amputation'. This portkey is valid only between 5pm and 6pm on the 29th. Bring several days worth of clothing and other essentials (should the meeting run longer than expected – the location has time compression wards). It is best not to make plans for October 30th.
This parchment is charmed with a secrecy and privacy spell. No one else can read it, and you cannot divulge the contents to anyone else.
Hope to see you then
Death To Voldemort
Clotho
It would be fair to say that the receipt of these letters caused much consternation.