When we discuss tone, what we refer to is the way the author seems to feel about his or her subject. Here, the author, Anthony Doerr, seems to feel sympathetic toward the protagonist, the hunter, and his wife, Mary. The married couple have been estranged for years, but neither one of them is presented as being strictly in the wrong or as having done something terrible or unexplainable. The pair simply do not understand one another: one drives and fuels the other, and yet they share a kind of pure and simple bond that seems to defy all of their differences.
Mary has a peculiar talent—to see the dreams of the living and the afterlife of the dead—and this is not a talent that her husband can relate to or comprehend; she left him one day when he continued to refuse to believe her. Now, some twenty years later, they do not need to speak to one another to feel their connection still. Both are presented sympathetically, as though we are not meant to judge the actions of either one because both are so candid.