By Blood (слэш)

After Bucky agreed to return to Avengers Tower with Steve when Hydra fell, he and Tony realize that his time with Hydra changed him far more than anyone could have ever guessed. Except Tony, who, by a quirk of fate, happened to be one of the few people on the planet uniquely suited to help Bucky out with his 'drinking problem.' But the past doesn't like to stay buried, and they eventually discover that the Winter Soldier project didn't really die with Hydra...
 
Bucky followed Tony as they continued down the hallway, JARVIS scanning the way ahead as far as his sensors could reach through all of this rock and metal and concrete. Then Tony came to a stop and some instinct made the hair rise on the back of Bucky’s neck.
“Holy shit,” Tony said. “Uh, James, we got a big fucking problem.” He stood to one side so that Bucky could stand next to him, and he had to stare for a minute before his brain could understand what his eyes were telling him. Unlike the previous rooms, this room wasn’t littered with leaves and trash; it was littered with bodies.