The second half of Grey’s Anatomy‘s 16th season — which kicks off Thursday at 9/8c on ABC — will feature a “really painful” storyline that delves into “mental health,” previews showrunner Krista Vernoff, who also describes the forthcoming plot as “beautiful and impactful and important.”

Vernoff declined to reveal which Grey’s character(s) the story will focus on, but Jo (Camilla Luddington) would seem to be a prime suspect given her past struggles with mental health and the fact that her marriage to Alex is presumably headed for upheaval in light of Justin Chambers’ abrupt departure. (Our interview with Vernoff took place prior to news of Chambers’ exit.) How Grey's Has Handled Major Exits

That said, the storyline in question could also very well center on Kelly McCreary’s Maggie, whom Vernoff confirms will be “in a very dark place” when Grey’s returns. “She’s never made an error that led to the death of a patient, and now she’s done it — and it was her cousin,” the EP notes. “People who love her have to rise to the occasion to help her.”

Thoughts/theories about who will anchor the storyline? Post ’em below!