Fan Casting Natasha Romanoff in MMU/6.: The Avengers (2012)

In this movie Natasha was a member of the Avengers but she was secretly a double-agent of Nick Fury. Her mission was to take back the Tesseract for S.H.I.E.L.D. so they could have build more special weapons. But she did not do her job, because Loki brainwashed her partner, Clint, whom with Natasha was in love. After she succeed to save Barton the duo foughts alongside the Avengers in the battle of NY.