O. Henry very cleverly plots his story "A Retrieved Reformation" so that Jimmy Valentine will be in his fiancee's father's bank with his suitcase full of highly specialized safecracking tools just at a time when a little girl gets accidentally locked inside the new burglar-proof bank vault. She is his fiancee's five-year-old niece Agatha. Jimmy is faced with a dilemma. If he rescues the hysterical little girl with his tools, something which only he can do, he will expose himself as a professional safecracker and not the respectable local businessman he has been trying to be under the pseudonym of Ralph Spencer. But if he doesn't break into that vault quickly, the little girl will die of suffocation. To make matters worse, his nemesis Ben Price, the detective, is watching from just outside the little room where Jimmy's fiancee and her whole family are gathered around the vault.
His fiancee Annabel Adams, who has no knowledge of Jimmy's criminal past, pleads with him:
“Can't you do something, Ralph—try, won't you?”
It is his love for Annabel that motivated Jimmy to reform in the first place. Now his love for Annabel motivates him to use his criminal expertise, even though he knows it will mean losing her love, losing the esteem of her family, and going to prison when he is arrested by the waiting Ben Price for the three recent bank jobs he committed about a year before moving to the town of Elmore, Arkansas..
He set his suit-case on the table, and opened it out flat. From that time on he seemed to be unconscious of the presence of any one else. He laid out the shining, queer implements swiftly and orderly, whistling softly to himself as he always did when at work. In a deep silence and immovable, the others watched him as if under a spell.
In a minute Jimmy's pet drill was biting smoothly into the steel door. In ten minutes—breaking his own burglarious record—he threw back the bolts and opened the door.
Agatha, almost collapsed, but safe, was gathered into her mother's arms.
Jimmy is a hero. He has saved the child's life. No one else had the knowledge or the tools to crack that state-of--the-art bank vault--but he did it in ten minutes. In a characteristic O. Henry surprise ending, Jimmy leaves the little room expecting to be arrested by Ben Price, who will now have Jimmy's tools to use as evidence against him.
At the door a big man stood somewhat in his way.
“Hello, Ben!” said Jimmy, still with his strange smile. “Got around at last, have you? Well, let's go. I don't know that it makes much difference, now.”
And then Ben Price acted rather strangely.
“Guess you're mistaken, Mr. Spencer,” he said. “Don't believe I recognize you. Your buggy's waiting for you, ain't it?”
Jimmy will have a lot of explaining to do to Annabel and her father. The reader is left feeling that everything will be all right. Annabel will forgive and forget his past because she loves him and because he acted so heroically. Her father will do the same thing because of Jimmy's noble act of heroism and because the banker will feel assured that his future son-in-law is completely reformed. Jimmy can continue to live in Elmore under the name of Ralph Spencer and will soon be a respectable married man with a family and a big house paid for by Annabel's wealthy father.