In the story, who can be considered the "good guys" and the "bad guys?"

I think that the greatness of the story is that it really
does not include the idea of "good" and "bad" guys.  There are human beings who are
capable of some fairly dark and intense elements if the conditions are right.  The
doctor is not a bad guy, in the broadest sense of the term. He comes there to help the
girl, to protect others from infection, and to solve a medical problem.  The parents are
not bad, on the whole.  They want their child to be healed.  The girl is not bad, but
rather wanting to conceal the fact that she is sick.  They are not bad people, but in
the alignment of circumstances and conditions, their dark sides are revealed.  The
parents are shown to be ineffective, at best.  The girl is revealed to be an intensely
driven and angry child.  The doctor's sadistic element is illuminated.  In the story,
there are not "bad" or "good" guys, but there is the capacity for some unsightly
elements to human nature that can be revealed under the right circumstances.  The will
to act is something that helps to bring about elements within human nature that are not
necessarily representative of the "better angels of our nature."   In this, Williams
constructs a story where terms such as "good" and "bad" become contextual, indicating
that human nature is complex and labels are not entirely
effective.