Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Contrite, Nostalgic, and above all, Sober
Because of the personal connections Fitzgerald had with his tale (see "Genre" for all the details), we see that Fitzgerald's attitude towards his story is very similar to Charlie's attitude towards his past. Charlie feels disgusted with and ashamed by his extravagant behavior in Paris years ago. Fitzgerald is looking back at his own past and feelingly similarly contrite. His wife, Zelda, had just been admitted to a sanitarium for psychological problems, no doubt brought on or at least aggravated by the destructive drama of their marriage and F. Scott's constant drinking. Fitzgerald believed that the stock market crash of 1929 and the financial depression that followed was the result of the irresponsible behavior of his generation in the 1920s – and he participated in that irresponsibility.
At the same time, we might identify in Fitzgerald that hint of nostalgia of which we accuse Charlie. Look at the way he describes Paris, where "the bistros gleam" and the "fire-red, gas-blue, ghost-green signs shone smokily through the tranquil rain" while "the Place de la Concorde moved by in pink majesty" (1.26). An interesting question, by the way, is whether this is the author's own viewpoint or Charlie's. What do you think about it?