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
Septimus clashes with Chater over sex and with Thomasina over mathematics, while Bernard sets Sidley Park on end with his theories about Byron.
Act II
Septimus escapes a duel, but not the revelation of his deepest secrets; Bernard is so convinced of his theories that he goes public with them.
Act III
Septimus realizes Thomasina's scientific insight exceeds his own, and also that his own feelings for her might be more than teacherly; Hannah exposes the fatal flaw in Bernard's theory.