Season twelvefeatured 16 actors appearing in a starring billing. All season eleven cast members returned for the twelfth year with the exception of Patrick Dempsey who ended an eleven year run as Derek in the previous season finale. After guest starring in 30 episodes over the past five years, Jason George was elevated to main cast status as Ben Warren.
Episode number: 01
Original air date: September 24, 2015
Plot: Three months later, Meredith struggles with her new living arrangements after moving back into her old house with Amelia and Maggie as, back at the hospital, Callie is forced to step up for a patient and become her advocate when the case of two young girls it by a train reveals a tragic reality while Bailey is unnerved when a candidate for the vacant Chief of Surgery position arrives at the hospital and her credentials force Bailey to question whether she has what it takes to be the Chief. Meanwhile, Arizona tries to find a new room mate and Jackson seems to be the only person not anticipating April's return from Jordan.
Recurring characters:Giacomo Gianniotti as Andrew DeLuca and Debbie Allen as Catherine Avery
Episode number: 02
Original air date: October 1, 2015
Plot: On her first day as Chief of Surgery, the pressure mounts for Bailey as she strives for perfection, but she soon realizes the struggles of being a leader when she pushes her attending too far when faced with a deadly pituitary gland tumour on a woman who has grown exceptionally tall while Meredith grows frustrated when she is forced to pick up the slack for the work Bailey left behind. Meanwhile, April is placed in quarantine when she breaks out in a suspisious rash, escalating her marital issues with Jackson while tensions mount between Stephanie and Jo when Jo begins to feel her peers are outshining her. Amelia and Owen struggle to navigate their romantic waters while Arizona learns that Callie has started dating.
Recurring characters:Giacomo Gianniotti as Andrew DeLuca
Episode number: 13
Original air date: March 10, 2016
Plot:Bailey, Callie, Meredith, Jackson and Jo travel to a military hospital to perform a risky and revolutionary procedure on a cancer patient and, with the all eyes on them, the pressure mounts as Callie's professional standing is put on the line and Meredith struggles with her friends pushing her to date again. Meanwhile, Ben makes a risky move when he takes drastic action to save a patients life, putting him on a collision course with Richard, while the E.R. is inundated with a cheer leading squad after a stunt goes horribly wrong, forcing Stephanie to reflect on her own teenage years. Elsewhere, Andrew pushes Maggie to go public with their relationship.
Recurring characters:Samantha Sloyan as Penny Blake