The staff tries to deal with physical and emotional trauma in the wake of the vengeful gunman's deadly rampage. Derek makes a spontaneous decision to resign as chief and return to surgery.

After weeks of concealing the fact she was pregnant, Meredith at last tells Derek and is finally cleared to return to her surgical duties. Cristina experiences post-traumatic stress disorder in the midst of an operation.

Issues surface when Derek's estranged sister, Amelia, visits unexpectedly. Meredith and Derek continue to try to ease Cristina back into surgery.

Things are hostile on all fronts when a visit to the obstetrician results in some disturbing news for Meredith and Derek, and Lexie loses it when she notices Meredith and April getting closer.