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.
Amelia arrives at Seattle Grace to beg Derek to help with the gliosarcoma case; Cristina and Owen have heated arguments during marriage counselling; Alex realises he needs to improve his people skills in order to be a good doctor.
The BAU investigates a case in Rossi's hometown, forcing him to revisit his personal and professional past.
Tori discovers that her friends have been secretly going to a fancy restaurant instead of playing in an annual ping-pong tournament.
Alan befriends a gay man at a single parent meeting, but he makes both Alan and Charlie doubt their sexual identities.