What is so fascinating about this book is that Atwood presents the reader with a series of different points of view rather than restricting herself to just one. There is of course the major voice of Grace Marks herself, but then there are the more objective, third person reflections of Dr. Simon Jordan regarding Grace and her case. In addition, however, there are ballads, newspaper accounts and even extracts from letters. These serve to present the reader with a true smorgasbord of different opinions and views that leave us in no position to present a conclusive judgement about Grace's involvement with the murder or not.
When it comes to the two key voices of Grace Marks herself and Dr. Simon Jordan, it is clear that Grace in her account of her story to Dr. Jordan is unreliable. She admits as much to the reader on numerous occasions. Note, for example, the following quote that comes after Dr. Jordan tries to get her to explain more about how she uses the privy:
And so forth, I say firmly, because And so forth is all he is entitled to. Just because he pesters me to know everything is no reason for me to tell him.
Even though this particular quote is related to something that the reader could argue is unimportant, at the same time it points towards the partial and unreliable account of Grace, and her desire not to tell Dr. Jordan the truth of everything that happened. Grace's first-person, personal account of what happened is therefore one that cannot be trusted, and out of the two main voices, the reflections of Dr. Jordan are presented as being somewhat more reliable.