the_debt_of_time

She spoke the words so carefully and specifically that Remus could not help but
wonder what would happen in fifteen years, and why Sirius could not know the truth about
his own witch until that time.
"I will," he replied and watched as a second tongue of flame shot from the wand
and interlinked with the first, making a fine, glowing chain.
"And, in regard to the future and the knowledge you obtain from me, will you defer
to my judgement and my requests?"
"I will." He nodded and watched a third flame emit from Dumbledore's wand,
wrapping its way tightly around their hands, binding the Vow—and Remus's life—in the
secrets.