the_debt_of_time

"Indeed, it would appear so." Dumbledore nodded. "Before you learn any
information, Mr Lupin, I must request that the only questions you ask would be in regard
to things you have already witnessed or will soon witness, mainly Miss Potter's scars and
the letter in question." He gestured to the witch, who was still clutching the letter in her
hand as though it were her lifeline, not at all delicately like she had done up in the tower.
"The future is fragile, you see, and while the letter indicates nothing can be changed, it is
such that I am not willing to risk it, whatever the reason. I would stake my own life on the
outcome of the future; do you understand, Mr Lupin?"
"It's about the war, isn't it?" Remus asked, burying the suspicion that Dumbledore
might have subtly just threatened him.
It had to be about the war. Why else would Albus Dumbledore stake his life on it?
Mia's letter—or Remus's letter, he supposed—had mentioned the war, mentioned lost lives,
and how she could not change anything or save anyone. According to the letter, his future
self had sent Mia back in time because he had been asked to.
"Mia knows what happens, and you don't want me to accidentally or intentionally
ruin the outcome."
"That is correct," Dumbledore replied.
"If the future is better, and the war is over.. ." Remus hesitated as he thought of
the most recent editions of the Daily Prophet. A family of goblins had been massacred three
days earlier, at least seven Muggles had been reported missing from Wizarding villages, not
to mention the very public attack outside the Ministry of Magic in which two Aurors and
three Muggle bystanders had been murdered. "I wouldn't want to risk it either. No matter
what. I understand, sir."
"Very good. I value your word a great deal, Mr Lupin; however, even though
Legilimency cannot be used against you, you are not invulnerable to other spells, torture,
or even the use of Veritaserum. The last of which I believe the two of you are most familiar
with?"
Mia and Remus innocently avoided eye contact.
"So, how do we avoid it?" Remus asked.
"A vow: an Unbreakable Vow to prevent secrets of the future from being revealed,"
Dumbledore insisted.