Natasha is a Red Room operative; she works with the Winter Soldier. They are the best, but she slowly notices his conditioning breaking down. Eventually, he cracks and she kills him, and is rewarded by her handlers with the Winter Soldier call-sign. Her work at SHIELD and with the Avengers is a very long under-cover mission for the Red Room. As the Winter Soldier, she kills the Avengers (including faking the death of SHIELD agent Natasha Romanov), and returns to the Red Room. The story is told by intercutting the modern under-cover operation (where the reader does not initially know she is the Winter Soldier) with the narrative of her past with the original Winter Soldier, James Barnes.