The IRA-types are heroes in this world. Moonlight prevails, both symbolically and actually, reflected in the stage lighting, dark with strange shadows. Given Circumstances Environmental factors. The play takes place on a wharf in a seaport town in Ireland. Since the Man is being picked up by a rowboat, we can infer a fairly clear, calm night, with occasional clouds passing overhead, per the dialog.
Several lines refer to a chill in the air.
The action takes place at late night, after moonrise. The time of night is and condition of moonlight has a profound effect upon the mood, creating a sense of mystery and danger. Economic environment has some importance in that the reward of one hundred pounds for the fugitive's capture represents a very significant sum of money to the Sergeant and his fellow policemen. It is enough money to motivate the Sergeant to put himself in harm's way to earn it, and even to call his ultimate decision into question at the end of the play. Political environment is key to the action.