"Remus, where have you been for the past twelve years?"
"That's a secret." Lupin gave his habitual, gentle smile, though to Sirius it looked pale and weak.
Lupin couldn't clearly remember all the places he'd been over the years. Twelve years had passed in the blink of an eye, like a misty autumn morning fog you couldn't grasp. She was like a gust of wind: she came and went, circling through his life for twelve years, then left cleanly, without even a trace of dust behind. Only her face, hazy in the moonlight, would occasionally flicker through his dreams, adding a touch of color to his pale, bleak memories. It had been a secret journey, and nobody knew where they had gone.
Set in the Marauders' era. Might be angsty. Remus Lupin pairing with an original female character. Everything else follows the original plot.
Filling in the twelve-year gap in Remus Lupin's life.