In Cold Blood Rhetorical Example I Have A Quick Question About Word Choice...?

I have a quick question about word choice...? - in cold blood rhetorical example

I write a paragraph about a figure of speech used by the author (Truman Capote in In Cold Blood). I want to focus on how you are navigating between two lines of history to focus completely independent. However, I can not with so-called name for the device. I know that this film across the tracks. What word / device should be applied here?