Ben Price is a tough private detective. He could be described as Jimmy Valentine's nemesis. He could also be described as the antagonist in the story, with Jimmy, of course, being the protagonist. Ben sent Jimmy to prison once before, and he goes after him again when Jimmy is released from prison and quickly performs three safe-cracking jobs.
These were the days before the federal government became involved in protecting banks. When the Federal Deposit Insurance Corporation was created under the Banking Act of 1933, it gave the federal government the justification to prosecute bank robbers. The FBI now protects all banks covered by the FDIC, and the FDIC insures depositors for up to $250,000. But that was not the case in O. Henry's time. The banks had to hire their own protection, and Ben Price was one of the private agents who specialized in bank jobs. Just as Jimmy shows intelligence in burglarizing banks, so Ben Price shows intelligence in tracking him down.
The losses were now high enough to bring the matter up into Ben Price's class of work. By comparing notes, a remarkable similarity in the methods of the burglaries was noticed. Ben Price investigated the scenes of the robberies, and was heard to remark:
“That's Dandy Jim Valentine's autograph. He's resumed business."
In one of O. Henry's famous surprise endings, it turns out that Ben Price may be tough and relentless but that he also has a kind heart. He manages to track Jimmy to Elmore, Arkansas, where Jimmy is living under the assumed name of Ralph Spencer. When Price sees Jimmy saving the little girl locked in the bank vault at the risk of losing Annabel and going to prison for years, he changes his mind about arresting him.
“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?”