The irony is that the sniper kills his own brother. The story is set during the Irish civil war in the 1920's. Each brother has chosen a different side on which to fight. During his battle with an enemy sniper, the author foreshadows the ending by showing how similar each shooter is. Both are good shots and both are on rooftops that are on the same level. Both seem to be experienced riflemen. However, once the sniper has killed his enemy, he begins to change. He looks over the rooftop, sees the people he has killed, and begins to feel sorry for what he has done. He begins to curse at himself and at the war. The irony is made complete when he decides he must see the soldier he has just shot. He risks his life, dodges machine gun fire only to discover that it is brother who is lying dead on the street.