: Jason George (Ben Warren) was promoted to a series regular. Giacomo Gianniotti (Andrew DeLuca) also became a regular mid-season.
: Tension peaks when Callie’s new girlfriend, Penny, is revealed to be one of the doctors who failed to save Derek. Penny eventually joins the hospital as a resident, causing friction with Meredith and Amelia. Relationship Turmoil :
: Miranda Bailey successfully campaigns to become the hospital’s first female Chief of Surgery .
: Martin Henderson joined the cast as Dr. Nathan Riggs, whose arrival triggers a dark history for Owen Hunt involving his missing sister.
: Meredith Grey adjusts to life as a widow, moving back into her mother's house with her "sisters," Maggie Pierce and Amelia Shepherd. A major mid-season arc involves Meredith being brutally attacked by a patient, leading to a long recovery and therapy.