Septimus clashes with Chater over sex and with Thomasina over mathematics, while Bernard sets Sidley Park on end with his theories about Byron.
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.
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.