The episode centers on a "mass casualty event" after a gunman opens fire at Pacific College. This triggers intense PTSD for the doctors, particularly because the trauma is so similar to their own recent experiences.
Disarm - Grey's Anatomy (Season 7, Episode 11) - Apple TV [S7E11] Disarm
: One of the patients brought in is Jared Swork, the shooter himself. This creates a moral dilemma as the doctors—specifically Meredith and Derek—are forced to save the life of a man who resembles the person who tried to kill them. The episode centers on a "mass casualty event"