Mia Montgomery is the younger sister to Addison Montgomery. In New York mia was having an affair with Derek shepherd. They fell in love and he was the only man that she had been with but when Derek left after finding out about mark and Addison it broke Mia heart and things weren't the same again
Mia decides to go to Seattle after Derek and they reunite. Mia is hiding secrets from Derek over what happened after he left New York and they decide to try and make a relationship work with the two of them but how long can they make it work especially when Addison turns up?