She's a fairly steely and steadfast character. Practical, pragmatic, no nonsense. So much so that we don't really know anything about Call the Midwife's Sister Evangelina's background.
All that, though, is about to change, promises Pam Ferris, the actress who plays her, when some of Evangelina's "painful" past comes back to haunt her.
"We don’t know much about Evangelina’s history," Ferris tells us. "I only know what I know from Jennifer Worth's book, that she comes from a comparatively poor family in Reading so I for myself have imagined lots of brothers and sisters and possibly that she was helping with births from early days.
"But we don’t know what happened to that family and she at some point felt that the church was the right place for her and dedicated her life."
One thing we do know, says Ferris, is that "she’s an extraordinarily courageous woman. She was parachuted into the front line at the end of the First World War when the survival rate of nurses, or anybody parachuting, was 50/50. Pretty amazing."
So what else might we find out about the grouchy nun in series three?
"I don’t want to spoil the surprise for you but some of her past comes back from before she became a nun and it’s very painful," teases Ferris.
Call the Midwife series three starts on Sunday at 8:00pm on BBC1