The plot starts with Tony being abducted by Hydra and given to Winter Soldier. They think he will kill Tony. Instead, he decides he likes and wants to keep Tony. Tony calls him Murder Kitten as a pet name. Bucky is very protective and makes the guards let him get salads and greens for Tony, since he is a vegetarian as a rabbit and can't eat meat.
I think they rescue themselves and run into Steve and Co just as they were coming to save Tony.
Either gen or Tony/Bucky.