The reference to "jimmy stewart" in this line is most likely intended as a/an allusion.

I believe its literary not completely sure sorryy

dramatic irony occurs when the reader/audience knows more about a character's situation than the character does. the one main effect is that it gives the reader a sense of superiority, or detached superiority. the reader not only seemingly discovers what is revealed, but feels superior for doing so.

from the excerpt from the "the dark game" the reader can infer that folke cronholm was spying for the allied nations.