What kind of mood does the ending of "After Twenty Years" create?How would you characterize officer Wells?
I would say that the mood of the end of the story is sort of sad and wistful. It is a mood of wishing that things had not changed -- that they used to be better than they were.
This is tied to the character of Jimmy Wells. He is still a good person like he was twenty years before. He is very honest -- so honest that he will not just let his old friend Bob go. He knows that Bob is a wanted gangster and he does not think it would be right to let him escape.
At the same time, Jimmy has too much love left for Bob to want to arrest Bob himself. Instead, he has another officer do the job.
Jimmy's action sort of sets the mood -- he surely wishes that Bob had turned out different and he wishes things were still like they used to be.