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
The curtains open on the huge funeral of Miss Emily Grierson, which is taking place on the grounds of a decrepit southern house. The fact that nobody in town has been in Emily's house for a decade sends the narrator spinning backwards down memory lane, from the tax collection mission ten years before, to the "smell" forty years before that.
This act ends with Emily reading the words "For Rats" under the skull and crossbones on her package of arsenic.
Act II
Act II begins with Emily and Homer riding through town in his buggy, and cycles through the town's various interference in their relationship, from the gossip to the preacher to the cousins, to the moment when Homer disappears forever into Miss Emily's house.
Act III
The final act opens with Emily opening her door, and letting in the little painting students, some years after the Homer Barron business. Then the door closes again. We see Tobe walking back and forth from house to marker, his hair graying, and we get occasional glimpses of Miss Emily through downstairs windows. Then we're back at the beginning at the funeral.
Before we close the old curtain for the last time, we have to come face to face with the rotting corpse of Homer Barron and the telltale strand of iron-gray hair on the pillow next to him.