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
In Act I, we are introduced to the Invisible Man and his strange behaviors. We also get to see how other people react to him (not well). Once the Invisible Man reveals himself as an Invisible Man, he can't go back to being just a stranger. That's when we really get to the good stuff. Read on!
Act II
Griffin goes through a lot (and puts everyone else through a lot), and in Act II, we get his back story. Maybe this will make us feel sorry for him. Or maybe not. In any case, after he recounts his history, Griffin is betrayed by Kemp. Being betrayed by Marvel is one thing, but Kemp was supposed to be a trusted friend. Kemp then uses all of Griffin's secrets against him; even the narrator remarks on how that must hurt (26.2). This is definitely the IM's low point.
Act III
From his lowest point (the whole world hates him), the Invisible Man makes a momentary comeback around Chapter 27. Instead of just giving up, the Invisible Man decides to take the fight to his chief enemy, Dr. Kemp. This could be a rousing after-school special on never giving up, except with a homicidal maniac as the star. Unfortunately, it doesn't work out and the Invisible Man gets killed. The end.