"A Retrieved Reformation" has a fairly standard plot structure in which there is a protagonist and an antagonist with a showdown between the two. Jimmy Valentine is obviously the protagonist. He creates the conflict by safecracking. Mainly he breaks into banks and uses his special tools and expertise to burglarize the safes. An antagonist is usually created by the activities of the protagonist. In this story the antagonist is a private investigator named Ben Price who specializes in protecting banks. The fact that Ben Price had previously caught Jimmy and had him sent to prison shows that he is a well-matched adversary. In a good short story the protagonist and the antagonist should be equally matched. Jimmy is a smart burglar and Price is a smart detective who knows everything there is to know about his specialty. The real conflict begins when Jimmy gets out of prison and goes back to his old ways. Price investigates three recent burglaries and knows that Jimmy is back at work.
“That's Dandy Jim Valentine's autograph. He's resumed business. Look at that combination knob—jerked out as easy as pulling up a radish in wet weather. He's got the only clamps that can do it. And look how clean those tumblers were punched out! Jimmy never has to drill but one hole. Yes, I guess I want Mr. Valentine. He'll do his bit next time without any short-time or clemency foolishness.”
What Ben Price doesn't know is that Jimmy has met a beautiful girl, fallen in love, and decided to reform. He is all set to arrest Jimmy in Elmore when he happens to observe the whole scene in which Jimmy sacrifices everything in order to rescue the little girl who is trapped inside the bank vault. This leads to one of O. Henry's famous surprise endings. The conflict is resolved when Ben Price decides to let Jimmy go free and retain his new identity as Ralph Spencer and the new straight life that goes with it.