Luna and Fay drank their distilled attention and stepped into the Repelling Section.
It was like when Luna was very young and her parents had taken her to Third Hand Book Emporium and told her she could have one book. Except this time instead of one book she had approximately five minutes before the distilled attention ran out.
"Check it out. Next year's The Historiography of Time Travel," said Luna.
"Focus. We're looking for books about the Department of Mysteries. Ignore everything else," said Fay.
Luna reluctantly tore her eyes away from Zeitsmithing, Wrackspurt Ecology and Counter-Zeitsmithing. They searched through the titles systematically.
"I found one. Magical Espionage: Theory and Practice. How much time do we have?" Luna said.
"Two minutes. It'll have to do," said Fay.
Luna and Fay were wary of drawing attention to themselves. The Hogwarts Library had charms to detect unauthorized removal of books. They opened the book on the stone floor and read it on their knees.
Table of contents:
Fundamentals of Magical Concealment
"Start with fundamentals," said Luna.
Fay turned to Chapter 1.
…If an adversary asks "Does a secret exist" then the secret has already been lost. Magical concealment therefore operates on the principle of (mis)directing attention.
There are a spectrum of spells for (mis)directing attention, from Muggle-Repelling Charms to memory modification. However, the most secure method of concealing a secret is Fidelius Charm. So little is known about the Fidelius Charm that we have fit the entirity of our researches into Chapter 7…
Fay turned to Chapter 7. She glanced at her watch.
The Fidelius Charm hides a secret in a single sentient being. It operates by cleaving consensus reality…
Fay began turning pages.
"But—," objected Luna.
"We have one minute of attention remaining. We need to know if the Department of Mysteries employs the Fidelius Charm," said Fay.
…However, the Fidelius Charm was immediately used in 683 CE to hide itself…
"That doesn't make sense. What's the point in Fideliusing the Fidelius Charm if the Interdict of Merlin already prohibits inadvertent transmission?" said Luna.
"The Interdict of Merlin prohibits indirect transmission. The Fidelius Charm prohibits all transmission," said Fay.
"Then there's no way for the Department of Mysteries to use the Fidelius Charm," said Luna.
"Why not?" said Fay.
"The Department of Mysteries is an organization. Organizations function by teaching their employees. If something cannot be taught then—," said Luna.
"Understood," said Fay. She turned the pages backward.
…operates by cleaving consensus reality. The connections are that which is sacrificed. A person placed under the Fidelius Charm, while protected, will be unable to interact meaningfully with consensus reality.
Luna stared into the wide eyes of her imaginary friend.
"Wait. If the Fidelius Charm's incantation was lost, then how was it cast on…" said Luna.
"Time's up," said Fay.
Luna and Fay suddenly realized they were late for dinner.