What is the author's tone in The Minds of Billy Milligan by Daniel Keyes?

The book is written in a fairly straightforward tone. There are times of hope and periods of hopelessness and these are shown with great clarity. The sensitive reader may find himself feeling that hopelessness simply because of the sheer monotony of Billy's personality issues. The constant switching of characters leaves him in some serious situations and it is sometimes possible to see a vague hint of humor though the majority of these times are filled with uncomfortable feelings and sometimes even danger.