The twist in the story's "tail" is only possible because Greene has constructed a narrative that seems to follow the reader's expectations only to undermine it at the end.  The reader is consistently reminded as to how the trial is a foregone conclusion and the defendant Adams will be found guilty.  Once the twin is introduced, this twist enables both Adams brothers to walk out of the courtroom.  It is in the ending, in the tail, where I think that the greatest twist develops.  In the commotion of freedom, the chaos makes it unclear how exactly one of the brothers was pushed into the street and thus run over by the bus.  It is here where the reader is thrown into chaos because of the death.  A few moments ago, there was a clear expectation as one of the brothers was exonerated.  Immediately following though, a death at the hands of a bus results.  It is here where a twist is evident.  Yet, I think that one can also find one more twist as the ending of the story does not focus on the trial or even on the surviving Adams brother.  While we do not know which Adams brother was killed, the one absolute is the sense of emptiness that Greene finds in Mrs. Salmon, who is left staring on at death in front of her.  Whether she will find the ability to go to sleep is the final twist in the "tail" or ending of the story.