The story begins with a theological discussion in an airship, whose owner, Lucifer, nearly runs it against the ball and the cross which surmount St. Paul's, London. Here he leaves the other occupant of the ship, an old hermit, who appears again at the end of the story. Then the reader begins to follow the adventures of two Scotchmen, Maclan, the romantic highlander and Catholic, and Turnbull, the rational lowlander and atheist. Because the latter has spoken disrespectfully of the Virgin, the former challenges him to fight, and the story becomes the record of their attempt to do so, in spite of the interference of a world which is too indifferent to either religion or atheism to allow a conflict for such causes.