Mary's Exit Was Nerve-Wracking For The Showrunners

Mary's unexpected exit takes place in the "Ghosts" Season 4 episode "Gone Gone," setting the stage for an installment that explores the concept of grief. All of the characters handle her demise in different ways as they attempt to make sense of what just happened to their ghostly friend. As viewers, we know the only reason Mary is gone is because of Katy Wix's decision to leave the show, but as far as in-continuity explanations go, we have no choice but to speculate on the details — much like Wix herself has.

During an appearance on BBC's "Inside...Ghosts" podcast (via Den of Geek), the Mary actor offered up her take on why her on-screen alter-ego moved on to the afterlife. "I sort of read it as philosophically that you have to heal something or conclude something or something needs to happen," she explained, theorizing that when Mary truly finds her voice in the Season 4 episode "Speak As Ye Choose," that represents her overcoming an obstacle that prevented her from reaching the afterlife in the first place.

Mary's farewell will endure as a landmark moment on "Ghosts," regardless of the canonical reason it happened. It's fair to say that the showrunners handled it as thoughtfully as they could.