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
Act I ends when Bartleby announces for the first time that he "prefers not to" participate in basic office tasks – the Narrator is committed to finding out what is up with this guy.
Act II
In desperation, the Narrator picks up and moves his whole practice to another building, minus one very odd scrivener.
Act III
The final act contains the fallout of the Narrator's decision to abandon Bartleby at the old office – he's carted off to prison and eventually dies.