Richard Wright in The New Republic:
I don't know what the book is about; the nearest I can come to indicating its theme is to refer to the Catholic confessional or the private office of the psychoanalyst. The characters, Negro and white, are “naturals,” and are seen from a point of view that endows them with a mythlike quality. The core of the book is the varied relationships of these characters to Singer, a lonely deaf mute. There are Mick Kelly, a sensitive, adolescent white girl; aged Dr. Copeland, the hurt and frustrated Negro; Jake Blount, a nervous and unbalanced whiskey-head; and Biff Brannon, whose consciousness is one mass of timid bewilderment. All these characters and many more feel that the deaf mute alone understands them; they assail his deaf ears with their troubles and hopes, thereby revealing their intense loneliness and denied capacity for living.
When the deaf mute's friend dies in an insane asylum, he commits suicide, an act which deprives the confessional of its priest. The lives of Miss McCullers' characters are resolved thus: Mick Kelly is doomed to a life of wage slavery in a five-and-ten-cent store; Dr. Copeland is beaten by a mob of whites when he protests against the injustices meted out to his race; Jake Blount stumbles off alone, wistfully, to seek a place in the South where he can take hold of realty through Marxism; and Biff Brannon steels himself to live a life of emptiness.
more here.