How does Stevenson create tension in the chapter the last night of jekyll and hyde?

To be perfectly honest much of the fame and hype about the story doesn't come from the novel but from the stage performance adaptation. The transformation of the good doctor into the fiend Hyde was a acting opportunity much exploited by the actors of the time, sometimes sending the more sensitive members of the audience (plants possibly) in to swoons and hurried retreats from the theater. In the novel Stevenson often (at least twice) goes into thematic episodes in which he does nothing but describe the surrealistic settings and actions. It was tangent already 'iffy' in a Victorian novel and would not at all 'fly' in a modern novel today.