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 grandmother warns that The Misfit is on the loose, but the family chooses to head towards Florida anyway. They set off and stop for lunch at Red Sammy's. The grandmother remembers there's an old plantation around here somewhere that she wants the children to see.
Act II
Car accident! The family is trapped. The Misfit arrives, and the grandmother brings down his wrath by recognizing him. As the grandmother talks with The Misfit, her relatives are shot in the woods. She starts to lose it.
Act III
Moment of grace saves the day, but not the grandmother. The Misfit shoots and kills her. He's left to think about what's happened.