Many of de Maupassant's short stories are loaded with irony, and this one is as well. Boule de Suif is a prostitute. She and many others are fleeing from the French city of Rouen to Le Havre during the Franco-Prussian War. Along the way, the other travelers treat Boule de Suif with disdain, ignoring her and acting very superior to her, because she is a prostitute. The weather is bad, the voyage slow, the passengers are hungry. No one has any food except for Boule de Suif. She kindly shares her food with the others. The coach winds up being stopped by the Germans and they will not let the passengers go unless Boule de Suif agrees to sleep with the head officer. She refuses, but finally, the other passengers convince her to sleep with him for the greater good. After all, she IS a prostitute, after all. She finally sleeps with him, the passengers are released, and they go on their way.
The passengers revert back to their former behavior of treating Boule de Suif like a second class citizen. They won't even share the food they now have with her. The prostitute is the good person, the other passengers are the bad persons. Things are juxtaposed, another quality of the story.
The passengers claim to be patriotic Frenchmen, yet they are fleeing like cowards. Ironically, Boule de Suif is much more patriotic than they are. The reason she refuses to sleep with the German officer is because he is a German, even though the passengers comment that it IS her job to sleep with men, after all.
The short story has interesting characters. The author gives quite a bit of information about the occupants of the carriage. They are hypocrites and cowards, however. Maupassant spends a lot of time criticizing them and their greedy, petty, bourgeois ways. Despite the fact that the passengers believe themselves to be superior to the priostitute, it is she that obtains their freedom. The noble one, after all, is the prostitute. Interesting, huh?