With the theme of "After Twenty Years" as Duty vs. Friendship, the character of Jimmy Wells finds himself placed in the difficult situation of having to perform his duty as an officer of the law on his friend from the past. Having recognized Bob as he struck a match to light his cigar, Jimmy makes the decision to feign non-recognition and continue on his beat so as not to arouse Bob's suspicions. In addition, Jimmy may have considered the fact that he does not have a gun on his person while Bob may be in possession of one (in the early 1900s, the setting of this story, beat policeman did not carry guns on them).
Having ascertained that Bob will wait for a while before he gives up on his friend, Jimmy reports in at his police station. In his letter, he explains his actions: "Somehow I couldn't do it myself, so I...got a plain clothes man to do the job," meaning that he does not have the heart to shame his friend by arresting him. While some may judge Jimmy as a bit of a coward, it seems more appropriate to recognize in Jimmy his tremendous respect for the value of friendship. He must do his duty, but he can do it in such a way that he does not embarrass his friend. Jimmy's actions demonstrate that he still cares for his old friend despite his crimes. In this way, Jimmy is true to both his office and his heart.