The central idea of this short story is that of transformation and change. The basic premise of the tale is that a father has returned to Paris to try and regain custody o fhis daughter after his financial ruin, the death of his wife and his own struggles with alcoholism. Charlie is a character who is desperately trying to present an image to those around him of somebody who has transformed his character, but the overall change in his character is somewhat undercut by the various details that Fitzgerald gives that suggest that this reform is not entirely completed.
These hints are made through various temptations that Charlie experiences to return to the "utter irresponsibility" of his previous life. On the one hand, the story begins with Charlie resolutely refusing a drink from the bartender and proudly saying that he has "stuck to it for over a year and a half now." On the other hand, we see how straight after this he makes us doubt his resolute nature by giving the bartender the address of the Peters so that he can pass it on to Duncan Schaeffer, who was an old drinking partner of Charlie's. These kind of examples abound throughout the text and again and again we are made to think that the transformation of Charlie from a dissipated alcoholic to a fine upstanding individual in business is not entirely complete yet.