bank jobs. Jimmy knows he would have to go to prison for a long stretch. His nemesis predicted what will happen to Jimmy when he catches up with him:

"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.”

If Jimmy was sentenced to four years in prison for burglarizing a bank in Springfield, he might get twelve years, without clemency, for the three jobs he pulled after his release. He would be a hardened career criminal when he got out again. There would be no chance of another reformation, or of finding another girl like Annabel Adams. Ironically, Jimmy risks everything by rescuing little Agatha from the bank vault, but because he risks everything by exposing his identity as a master safecracker, he is allowed to "retrieve" his reformation.

“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?”

In O’Henry’s story, the character of Jimmy Valentine is a safe-cracker and career criminal. As the story develops, Jimmy leaves that identity behind. Arriving in Elmore, Arkansas after being released from prison, his love for Annabel Adams changes him into a different person. He even changes his name to Ralph Spencer. The reformation he undergoes includes opening a legitimate business, succeeding in operating it, and becoming engaged to Annabel.

All of this is placed at risk, however, when two things occur: detective Ben Price tracks him down, and a little girl’s impulsive trick jeopardizes her sister’s life. While Jimmy/Ralph is in the bank with Annabel and her family, her father—the bank manager—is showing off his fancy new safe. One of Annabel’s little nieces mischievously shuts her sister, Agatha, inside it. Jimmy is forced to reveal his safe-cracking skills in order to rescue the child. Jimmy stays true to himself by using his skills but also by tapping into the good inside him, even though it means risking his future happiness. Fortunately, Price understands this and passes on the opportunity to capture him.

Jimmy's main problem is that he is stuck with the burglar tools. His ability to open the vault to save the little girl proves he is Jimmy Valentine, but Ben Price could not arrest for that. The specially made burglar tools, however, could be used as evidence to prove that they were used on the three safecracking jobs described in the story.

A week after the release of Valentine, 9762, there was a neat job of safe-burglary done in Richmond, Indiana, with no clue to the author. A scant eight hundred dollars was all that was secured. Two weeks after that a patented, improved, burglar-proof safe in Logansport was opened like a cheese to the tune of fifteen hundred dollars, currency; securities and silver untouched. That began to interest the rogue-catchers. Then an old-fashioned bank-safe in Jefferson City became active and threw out of its crater an eruption of bank-notes amounting to five thousand dollars.

Jimmy, of course, could lose Annabel when she found out he was a professional safecracker, but he couldn't have revealed his real identity if he hadn't had those special tools. The vault would have been impregnable without them. O. Henry takes pains to tie Jimmy to those tools throughout the story. Initially, Jimmy takes them out of their hiding place and looks at them. After that he is shown carrying the suitcase numerous times, and the reader knows what is in them. O. Henry arranges the plot so that Jimmy has to carry that suitcase right inside the bank, so Ben Price is able to catch him red-handed. Fortunately, however, Jimmy's good deed saves him from going to prison (although he might have a hard time explaining to Annabel and her family how Ralph Spencer just happened to have a suitcase full of burglar tools with him that morning and how he just happened to be so adept at using them).

He looked at her with a queer, soft smile on his lips and in his keen eyes. 
Annabel," he said, give that rose you are wearing, will you?"
....Jimmy stuffed it into his vest pocket, threw off his coat and pulled up his shirt-sleeves.  With that act Ralph D. Spencer passed away and Jimmy Valentine took his place.

By saving Agatha from death in the bank vault, Ralph Spencer has been destroyed; the persona with which Annabel Adams, daughter of the owner of the Elmore Bank, has fallen in love. Having destroyed Annabel's trust in him, Jimmy assumes that she will no longer love him. However, she may be moved by his tremendous act of charity in his rescue of the little girl from the vault in which she could suffocate. For, as he walks away, he hears a soft voice calling, "Ralph."

Yet, if Jimmy Valentine were to have pretended that he could not open the safe, his conscience would have bothered him because, as the warden told him when he was paroled, he is "not a bad fellow at heart"; moreover, he would have risked being found out as a bank robber when Ben Price would surely have arrested him, then.