Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Grieving, Angry, Fatalistic
Why? Why?
Since four well-loved people have just been brutally murdered, a tone of grieving permeates the early pages of the book. When the narrator describes Nancy Clutter setting out her dress for church the next morning—clothes that she'll actually be buried in (1.198); or after Herb Clutter's friends, having cleaned the rooms in the house in which the murders have taken place, burn the blood-soaked bedclothes, watch the smoke rise to the sky, and wonder about the value of a virtuous life (2.7), it is enough to make a reader cry.
Why Me!?
Perry's anger about his family life could fill a book, and almost does. Perry's sister Beverly isn't much happier:
As though life for [Perry's] brother and sisters had been a bed of roses! Maybe so, if that meant cleaning up Mama's drunken vomit, if it meant never anything nice to wear or to eat. (3.131)
The anger in the book comes almost completely in first-person reports. In between the methodical descriptions of the investigation, townspeople vent their anger at the killers and the killers rage against the unfairness of life.
No Use Wondering Why
At other points in the book, a tone of fatalism—the idea that people have no power over what happens to them—takes over. When, in the first chapter, the narrator discusses the "four shotgun blasts that, all told, ended six human lives" (1.5) the fact is stated without emotion, just as fact. Similarly, when Myrtle Clare says that "You live till you die, and it doesn't matter how you go; dead's dead" (3.146) her statement isn't filled with tears. It is a statement of resignation. And don't forget that inscription on Bonnie Clutter's bookmark. Our days are numbered and we're not the ones doing the counting.