Jimmy Wells (Patrolman Wells) is a loyal and trustworthy friend. He was at "the appointed place," but couldn't bring himself to arrest his friend.
"Silky" Bob, might be considered a loyal friend too because he showed up "After Twenty Years" as well. The difference is the two paths that each took over their lives. Bob became a thief while Jimmy led a more honorable life.
Jimmy is portrayed as the protagonist of the plot. He has been shown as somebody who is torn between his affection for his friend and the call of duty. In a roundabout way, he has been given the subtle role of the antagonist of the plot as well. Because the only "evil thing" of the plot, so to say, was the arrest of the "friend" who came to visit an old pal his. Jimmy proved to be a person of mettle in the end who preferred duty to friend.
However, Jimmy's actions are justified in the narrative as "Silky Bob" turned out to be a thief. But, as "Silky Bob" too kept his promise, he too, has been shown in a positive light, notwithstanding his profession.