What secret is Evvie keeping from her best friend, Andy?

In Chapter Four, the reader learns that Evvie never told Andy the truth about either the unpleasant nature of her marriage to Tim, or about the fact that she had been packing the car to leave Tim for good on the day he had been killed in the car accident. This secret weighs heavily on Evvie, causing her to think of herself throughout the narrative as a "monster," (28) among other unkind self-judgments.