With tone as the attitude of the author towards his narrative, O. Henry seems to adopt a rather whimsical, amused, and light-hearted tone in "A Retrieved Reformation."
In the exposition of the story as Jimmy Valentine is released from prison, the warden encourages Jimmy to reform, saying with good humor:
"You're not a bad fellow at heart. Stop cracking safes, and live straight."
"Me?" said Jimmy, in surprise. "Why, I never cracked a safe in my life."
"Oh, no," laughed the warden. "Of course not. Let's see now. How was it you happened to get sent up on that Springfield job?...was it simply a case of mean old jury that had it in for you?...."
Further, O. Henry's narration exhibits a light-hearted, humorous tone as exemplified in these lines:
One afternoon Jimmy Valentine and his suit-case climbed out of the mail-hack in Elmore....
Jimmy collared a boy that was loafing on the steps of the bank as if he were one of the stock-holders....
Even when Jimmy finds himself in an emotional crisis at the bank as his beloved Annabel pleads with him to try to do something to save little Abigail who has locked herself in the safe, there is a whimsical tone to the narrative. For, Jimmy unpredictably asks his fiancée to give him the rose that she is wearing before he pulls out his safe-cracking tools.
Then, after Jimmy breaks open the safe and little Agatha is rescued, he calmly puts on his coat and walks toward the front door of the bank, having lost all hope of marrying Annabel and living a happy life. Yet, when Detective Ben Price stands in his path, Jimmy smiles, and in tolerant amusement, he greets the man who previously has sent him to prison, "Got around at last, have you? Well, let's go." But, O. Henry maintains the upbeat tone of the light-hearted story as Price ironically replies, "Guess you're mistaken, Mr. Spencer," and Jimmy Valentine/Ralph Spencer "retrieves" his reformation.