This is a major role.  Sam is the narrator, but the story is focused around Clara and her journey to become part of the Vigil.
We don't know a lot about Clara, except she is a loner and estranged from her family. She also possesses "the gift",  A talent for magic that not only makes her eligible to become a member of the Vigil, but also makes her a target and pawn of the necromancer romancing her in order to gain her trust. She is an ordinary young woman about to become a part of something she could never even have imagined. I see her as in her 20s, kind of reserved (although she gets over that very quickly.) It takes a lot to earn her trust.  She's a bit rough around the edges.  She should sound young but not naive.  She's had a less than happy life so far.  Whoever takes her on should be prepared to do a fair bit of screaming in the first issue.  heh.  I hadn't really thought she would have an accent but we really don't find out where she is from so... I'm open.  Clara also isn't everything she appears to be.  But that would be telling...