In the season premiere, the hospital staff is trying to deal with physical and emotional trauma in the wake of the deadly rampage of a vengeful gunman. As Dr. Perkins, a trauma counselor, is brought in to help in the recovery and to assess each doctor's readiness to return to work, Derek makes a spontaneous decision to resign as Chief and rushes back into surgery, taking everything a little too fast, and Cristina buries herself in her wedding planning.