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
A gentleman caller is needed; Laura is shy; Tom wants to leave the family.
Act II
A gentleman caller comes; Laura stops being shy; Tom hints he is about to leave the family.
Act III
The gentleman caller is engaged to be married and leaves; Laura retreats back to shyness; Tom abandons his family.