For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Joe Christmas is adopted by the McEacherns, where he has Christianity literally beaten into him every day. One day he fights with McEachern, hitting him over the chair and possibly killing him. He steals money from Mrs. McEachern and runs away, roaming from town to town, a rootless drifter.
Act II
Joe Christmas arrives in Jefferson, Mississippi, shacks up with Joanna Burden, and starts selling whiskey illegally. When Miss Burden tries to reform him into a Christian black activist, Christmas becomes enraged, eventually killing her with a razor.
Act III
Christmas is murdered. Hightower has moments of deep insight in his study, realizing his selfishness and life's mistakes. The novel doesn't specify whether or not he dies. Lena Grove, Byron Bunch, and Lena's baby travel to Tennessee together in search of Joe Brown.