I can remember most of the plot for this fic, and I would've sworn I had it saved, but I just cannot find it anywhere. The story started not long after CA:TFA. Peggy and, I think, Howard find the Winter Soldier. They manage to get through to Bucky, but due to some chip in his brain, a kill switch maybe, they can't fully free him. Because Steve is "dead" by now, Bucky agrees to go back to the Red Room as their double agent. Peggy has a code phrase, something like "come in from the cold", that triggers Bucky's personality. Over the next few years they'd meet up and she'd debrief Bucky on the Winter Soldier's missions. He also developed a friendship with Erik Lehnsherr because he could fix the arm. Later, he's introduced to Peggy's protege Marcus, the future Nick Fury. At one point, the Winter Soldier is on a mission with Black Widow and she accidentally triggers Bucky awakening, but Coulson shows up to debrief him. She uses the phrase again later when she's escaping the Red Room. Then during present day, Loki for some reason removes the chip in his brain, allowing Bucky to stop being the Winter Soldier. He visits Erik to find out what all has happened.
I've been looking for this fic for a while, and no matter what variation of search terms I use, nothing pops up. Hopefully someone here recognizes it because it was such a great story, and I would love to read it again. Thanks!