I've got a book that I can't find the title for too. I thought it was by Charles Williams, but it might have been one of the other Inklings .... or just somebody my mind connected with them. It starts with a gal who has been afraid all her life of somebody who follows her in the shadows. A friend (in theatre?) finally gets her to talk about it, and through sharing her fear, she is able to let the "follower" actually meet her .... and it turns out to be herself. And it turns out that she has been bearing some of the pain/fear for an ancient ancestor who was burned at the stake as a martyr.
None of the Charles Williams titles I saw looked like the right book -- but maybe I just didn't recognize it! Anybody know?